Aim is very important. You can go a long with just the skill to aim well. The best way to practice that, is to play on Deathmatch servers. Prefer the ones where you can spawn all around the map, rather than in regular spawns, and prefer regular maps as well, so you can apply some same face-off plays on normal play you might learn in deathmatch. It's a totally different game there though. The skill level there can be very low (or adequate if you're lucky). You have no objectives and there's also a better chance to get to the back of your opponents or otherwise catch them off guard. Something you won't come across on a regular game of CS:S.
You can learn to aim very well on normal games as well (you can also learn a lot of other stuff, opposed to deathmatch), it's just that you get a lot more repetition, more heads to hunt, quicker actions and so on: Through repetition the action of aiming becomes more automatic. You don't even need to think about it and you've got your crosshair where it should be.
Pay attention where you are aiming at the current time, also when you move: It's a common mistake to run around aiming at the ground 2 feet in front of you. It's a long way from there to the corner where the enemy might be approaching.
Try not to get excited/frustrated/angry. It can ruin your game. If you get shot by an AWP and it seems like he was just lucky: It doesn't matter. You get to be lucky at times as well. On the other hand, if you're facing 4 enemies alone, being the last one of your team, and manage to kill 3 of them, and you have began to tremble with excitement, you'll have a harder time catching the last one. Leave the cheers to the end of the round.
Know where the enemy is. Know where you're teammates are. Some players can actually tell where their enemies are, even though they haven't even seen a glimpse of them:
A flash was thrown there (without a 'fire in the hole' or from a place you know your teammates can't be at).
A teammate got killed. I know where he went so.
I heard an AWP there.
An enemy shot at me and went back to cover again. Now he's back, nope. It's a different model/nick/weapon so it's another enemy. There might be even more than two of them.
If they were to come that way, they would already be here.
That's the sound of two footsteps.
And so on... Some players guess where the enemy is coming from. Some players know, because they think.
Try not to get edged out. Try to get that edge yourself If an enemy with an AWP is keeping a look at on open space where you're going to go next; he has the edge over you. You know it'll take a one in a million shot with the deagle to get him down before he does that for you. So, do something different instead: try to flash him or go another way.
If you're on an area where there are several places to keep a look at the approaching enemy, and all the enemy has, is a spot to peek and try their luck from: You've got the edge. If you were the enemy, you'd do anything to get pass that peeking point (with flashes, suppressing fire, smokes...), because after you get pass that, the enemy will no longer have the huge edge over you.
Kind of the same thing with bomb places. If you know there are 5 CT's guarding A, then go B, because you know there's only 2 of them tops watching that. Then you'll have a better chance going there.
Look at the scoreboard occasionally, especially in the end of the round. It helps to know how many enemies you're facing and if you have teammates still alive.
More importantly, look at the clock occasionally. If you don't complete the objective until the time runs out: you lose.
It might help if you've tweaked the game to run in DirectX 8.1, having every quality option set to 0 or off / have the best config for you, have a 120hz monitor, a million dpi mouse, are running the game in 500fps, have a 200 ? sound card with an excellent headset. But even then it's more about what you're used to, and these kind of (minimal) differences are enough to create differences amongst the very best. Then again, if a moderate player were to play with that kind of a setting against a better player with a worse computer, having default settings, 60hz monitor, and clocking 50 fps, at best: The better player would still probably win.
Just a couple lil' tips more:
Don't be afraid! You can go to places as the first player instead of blocking every other player when you decide "I don wanna" in a narrow doorway.
Kind of on the same subject: If you're rushing somewhere, you can really go rushing and very hard there: straight running, throwing flashes, it doesn't matter if you get flashed, the enemies will be flashed as well and running for cover. That's a good way to take many for a surprise, as many players won't be expecting that.
Pick your targets: If you've got to the back of your enemies, you might want to take your time and headshot the one running around, instead of that AWPer on deep concentration, not to mention that AFKer, whose the least threat to you.
I suppose that's of some use. Just the first couple things that popped into mind.
ratio of 1 kill to 4 deaths, but there has to be some way to play the game right. I haven't spent the 2 minute respawns staring at a wall. I take cover, fire in short bursts, stick with my team, look away from frags, and have been generally playing it safe with no avail. I still get gunned down, time after time. I don't know if it's the weapon choice(I stick with the main assault rifle, or the Bullpup AUG if I'm feeling bad and the Night Hawk(Desert Eagle) for my secondary) or my patience(slowly edge out of corners, fire off a few rounds, miss, get sniped by an AWP). 
