*New
I plan on organizing this better, and I'm currently debating making an actual guide, complete with my stratbooks (used from 2003-2008 by my actual teams in competitive leagues) completely for free and downloadable from any free mirror I find.

1. I will not blame, change, or research config files, resolutions, sensitivity, or any other game configuration.

This isn't so much a tip as it is a promise. There are professionals who play on every resolution, high sens, low sens, default key bindings, insane keybindings, etc. I promise HeatoN did not google "good counter-strike configs" on his quest to become a pro cs player. He picked settings, found them comfortable, and just focused on playing and perfecting his game. Being good at CS is about consistency. No one cares if you have an amazing game here and there. I'd rather have a player on my team who does well every match, rather than one who is either amazing or awful. The more you change your settings, the more inconsistent you'll be.

2. Consistency

I've stressed that consistency is important, but it goes deeper than keeping the same settings. For example, make sure you are able to sit comfortably at your chair/desk and make sure your chair position and height is the same every time you play. Most people don't notice or realize when you are anxious, you'll lean forward. If you're tired or sad you'll slump. This makes micro changes in the physical aspect of cs, as well as makes your mood change your game. This brings me to my big idea.

Muscle Memory

I haven't read anything about this in relation to CS or gaming in general, which surprises me. Reflexes are a big part of cs, and reflexes are improved through the training of your muscles. To help you understand this better, let me give you an example. In basketball, if you haven't played for a year, pick up the ball and shoot - odds are you're going to miss. It'll go long, short, left or right, or even a combination. The more you shoot, the more you'll make and the more likely you'll miss by small margins. Why? Muscle memory. After shooting from the same distance for awhile, your body knows how hard it needs to throw the ball in order to get the ball into the basket. You can take a 15 minute break, and still your body knows exactly how hard it needs to throw it. Your body learns through repetition. Any task you do constantly becomes easier. This applies to CS. If you play the same spot on maps, you'll eventually learn how high you need to aim at a corner to get a headshot. But if you deathmatch with this knowledge, you body will learn how far your hand/arm needs to move in order to shoot some one at the far left of your screen. Eventually you will just automatically snap your crosshair on top of an enemy because your brain sees he's all the way at one side, and your arm knows it needs to move a certain distance to put the crosshair there. Bam. Science. This encourages you to keep your body in the same position every time you play. Any change to your settings or body position will cause your body to have to re-learn all of the movement distances. Do not change anything. Remember everything.

CS is a mental game

Lets put aim aside for a second. CS is about winning each round individually. You have 4 other players on your team. You do not have to kill everyone. Having more kills than your teammates does not make you win. The real trick to cs is not learning how to get more kills, but how to get less deaths. On CT side, most people defend their spots with the thought "if they rush my position, I'll be able to kill a few from where I'm hiding." This is wrong. What you should be thinking is "If they rush my position, I'll be able to kill or weaken a few while still being able to fall back and live." CS is a numbers game. 5v5 is even. 3v5 is outnumbering. A man with 1 hp can still kill 5 enemies. It's unlikely, yes, but it's possible. If you're dead, you won't get anything. Make sure your whole team plays this way. This doesn't mean play so passively that you end up saving every round, or let teams rush your site and plant, but don't let them do it without taking heavy damage. If you can adopt this play style AND learn how to retake sites, you'll dominate every match.

Slumps

They happen to everyone. So your aim sucks today. Big deal. When some one notices their aim is off, these happen:they get frustrated, spray more, and play more recklessly. All bad things. What you should do is stop trying to be the fragger and adopt a support role. Be the first to rush in when rushing a bomb site. You may die first, but if you're not aiming well, you put teammates who are aiming well in a bombsite still alive. The object is to win, remember? Also, just like in sports. If you aren't shooting well, start passing. Throw the flashes your teammates need, be the distraction, etc. Don't let bad aim make you a useless player.

Aim

Finally. The truth is, some people naturally aim better than others, period. You can practice all day every day and not be as good as that one kid on your team who plays an hour a day. Deal with it. However, you can become damn good. Assuming you read the muscle memory section, you know your body position and repetition are key to aiming well. But there are other ways: Set up a routine. When I was playing very competitive on a team and I knew I had to play amazing in order to win, I developed a routine. First, I would stretch, especially my hands, even if it meant just shaking them for 30 seconds. Then I would join a random dust2 pub server. I'd fool around, not taking anything too seriously, but just adjust to the game for 10 minutes. Then I'd put on music, and deathmatch. DM servers are amazing for aim because it quickly develops muscle memory but also is non-stop aiming, which makes your brain memorize head-level. It also helps your decision making skills. You have to decide whether to burst or spray. There is zero downtime, so you can practice ONLY bursting (which is what I do).

Composure

You'd be amazed at how much people spray in this game. The AK47 takes 4 bullets to the armored chest to kill some one. It takes one bullet to the head. While you're spraying your 10 ak bullets trying to get 4 in my chest, or basically to hit enough bullets to kill me, I can take a split second longer to aim for the head, and kill you. Yes, I'd take a lot of damage, leaving less than 50 hp. But I'm alive, you're dead. If you were to spray back there is a 50% chance you'd lose.

1. Knowing your reflexes.

Some people react quick, others slow. Knowing how quickly you react should determine your crosshair position. If you're waiting for an enemy to come from behind a corner, and you have your crosshair ON the corner, if you have bad reflexes you won't react until their entire body has turned the corner. Then you have to move your mouse and re-aim to try to shoot them. This is bad. If you react slow, give your self a half an inch between the wall and your crosshair. So by the time you react to the fact that they turned the corner, they will be in your crosshair.

2. Basic memory

This is really simple, but it helps to read it: know where to put your crosshair. This means know how high is head-level so you don't shoot over their head, or in their knees. This takes practice, but if you play catwalk on dust2, you probably play less than 5 different defensive positions, take note of a mark on the wall or any hint as to where to aim. A trick I do when I play cat, I'll sit back on ramp and let my teammate run down the stairs and I watch where head-level is. Because there will always be a time I will have to aim there. Other things to realize are where most people hide. If you're T side on dust2 taking the B site. You should realize where most people play. Platform? clear. Between platform and greenbox? Clear. Back site? Clear. Window? clear. Door? Clear. Immediate left corner from tunnel entrance? Clear. By this point you should be thinking he's out of doors or in closet. Checking each spot and EXPECTING THEM TO BE EVERYWHERE YOU CHECK. Will make your body be tense, and therefore react quicker. Also, if you expect them to be where you check, your crosshair will be in perfect position to headshot them if they do turn out to be there.

3. Goldfish memory

This is more of a trick than a tip. Goldfish have very bad short term memory. Every 30 seconds they completely forget what happened. This applies to CS too. The only way I can explain it is to give an example: Let's say you are CT side on dust2 playing bombsite B. Let's also say the T side sends 1 player B every round as a default strategy on gun rounds. First gun round you hide in closet at B. He comes out and you shoot him. Next gun round he comes out of tunnel, you kill him from closet again. The third time he comes out of tunnel. He expects you to be closet, so he doesn't check anywhere carefully. But you're not closet. You're hiding back of site and you see him check closet and shoot him in the back. Next gun round, guess where he won't check again? Closet. Yes, he died to you 2 times from closet and only once from back of site, but in his mind, you are just in random positions. So the next round, if you play back in closet, he won't check as aggressively as he did the 2nd and 3rd time. So the basic idea is to play with their expectations. If you play in the same spot every round, they know you'll be there so will check it more aggressively. Also, if you play in a new spot every round they'll check EVERY spot aggressively. So the idea is to make a pattern of 3 places. For our closet example. If you play in the corner directly right (from tunnel) of double doors, which is near closet, you won't be where he expects you to be, even if you are immediately next to it, this will throw him off and give you a split second advantage, which is all you need to shoot him in the face.

*Strat-calling

While it's easy to watch pro demos and take notes, odds are they won't work for your time. Firstly, your team doesn't have the aim they do, and therefore cannot play as aggressive as they do. To form strats, you must find your team's strengths and weaknesses. Personally, I play very aggressive, but the last team I was on all played a lot better when we played at a very slow tempo. Therefore, our strats revolved around me being a distraction or a buffer. We would run a default setup which would be 1 person scouting different parts of the map. During the first gun round, we would see how each position was played. Do they push cat? do they push long? etc. We'd find the weak spot, or any spot being played passive by a single person, and that's where I would target. I'd let them be aware of where I was. My team would wait for pushes, but any decent team would hold their ground. That's when we'd regroup. We'd take a site, and my job was the buffer. I slowed or prevented the team from rotating. If I'm near DD, they can't send all 5 people to the site, in fear I would flank behind them. People are also desperate for kills, so 1-2 players would shoot at me in mid, wasting precious time. I didn't need or try to kill them. I put bullets into them, but made sure to stay alive, because with me dead, that makes 1-2 teammates have to rotate over to watch their back.

CT side strats are similar. I've never been a strong awper, and I always forced my team to have a SINGLE dedicated awper. One person could awp, period, we didn't pick up awps if he had one. So my strats were based upon retakes. In practice games we'd often let teams take sites and plant to work on this. We'd play in positions where we could deal damage and fall back and save nades. We'd each have nade assignments. Everyone had specific places to throw their grenades. We'd retake, and people would have specific places to check to ensure the site is cleared. We did so well at retaking that this allowed us to play with bigger risks such as stacking sites. If we all played A and they went B, we could retake effortlessly as practiced. But if they all went A and we were at A, it was a quick round of domination.

But again, this depends on your teams strengths and weaknesses. If your team has great aim, play fast and aggressive with minimal grenades. If your team is more intelligent than aim-oriented, play at a slow pace. If you have a well balanced team, mix it up. Play super aggressive two rounds, then passive the next. Teams will become confused and have to develop a cautious pace. They see you rush out twice, so the next round they sit back and wait - while the next round you too sit back and wait, making them waste grenades and time.

Spraying
Though I've discouraged spraying often, it is still a skill you must master, moreover, if you do master it you become nearly unstoppable. The trick I use is aiming with the top part of the crosshair, the part that looks like "|". I start aiming with that after I've shot about 5 bullets. If I'm shooting the AK I try to put the top part of the crosshair on the left side of the enemy's head. If I'm using the colt I put it on the right side of their head. This is due to the spray pattern usually aiming in a 7 or backwards 7 pattern, with the AK going to the right - pulling to the left would counter this and most likely end up being a headshot. The colt is a bit weirder, as it goes left right then left again, but far less to each side than the ak, being more in the center.

Feel free to ask questions.
*I don't know if the site is bugged or something, but my profile says I have comments in this blog, but I can't see any. So if I don't get back to you, shoot me a message or something.