• Don't shoot and move (including jump) at the same time.
• Don't hold down the fire button for an extended period of time.
• Keep your crosshair aimed at head height.

I find these three general strategies have consistently over the years benefitted me in playing counter strike better.

Don't shoot and move (including jump) at the same time.

While your character is moving, your accuracy is greatly reduced. It is almost always better to stand still (or crouch) while you shoot to increase your accuracy. The only time I would be moving and shooting at the same time is if the other player is very close to me (within knifing distance). If you are under fire, there are two strategies you can use to stand still while you shoot back at the enemy while taking fire. The first is to "stutter step". By this I mean, move a little bit, stop and shoot, then move a bit then rinse and repeat that process. The other strategy is to be hiding behind a wall and then follow the stutter step strategy I mentioned above. If you find yourself in the position when you are wide open under fire you will probably die, no matter how good a player you are. Try to avoid these situations by using flashbangs and smoke grenades.

Don't hold down the fire button for an extended period of time.

This is a mistake a lot of newer players make, they see an enemy and quickly unload an entire clip. Because of the recoil in the game, it is very hard for even experienced players to accurately shoot an entire clip - try it yourself on a wall. The method I use is to instead shoot a bullet or two stop and then try again. This works very well in conjunction with the stutter step strategy I described above.

Keep your crosshair aimed at head height.

One of the strategies I use to more consistently hit a player's head is to keep my crosshair always aimed at "head height". If you watch streams of some of the pro CS players, you will notice they tend to always have the crosshair aimed at head height rather than the common chest height. A good way to keep your crosshair at head height is to aim at an ally at the beginning of the round, and to try and keep it at that y-position. Some maps, like dust, have bricks. I use the brick lines as guidelines on where I should be aiming my crosshair. The hardest place for this to work is on areas with elevation changes - so watch out for those areas. As another note, if you know the enemy is weak (has 20 hp left or less) it is more beneficial to aim at the chest as that is a larger area to hit and you will be guaranteed to kill them with one bullet. Also, if you are using the AWP, it is better to shoot at the chest rather than the head because the AWP 1 shot kills and the chest is an easier target to aim for.

I answered a similar question to this: How Do I Get More Guns?. Noticed that your question was posted a few hours before that though.

This is the new "Arms Deal" update which went live on 14/08/2013. Valve released a really good FAQ on it, which can be found here.

The bits of interest for your particular question, "How do I get item drops?":

• Timed weapon drops, just by playing on official and community servers (VAC enabled) in any game mode.
• Opening dropped weapon cases with a weapon case key.
• Trade weapons with other players through Steam's Trading interface.
• Purchase them from other players through the Steam Marketplace.

Regarding the first point, these are obtained for play time over the course of a week. As your play time increases, the drop rate will slow down. This is reset when the week rolls over. Not sure the start day or time of a week though.

I'm not 100% sure where you will get the weapon case keys. The below quote suggests that you buy these:

This update will also actively support the CS:GO competitive community with the introduction of the eSports Weapon Case. A portion of the proceeds from sales of eSports Case Keys will go towards prize purses at competitive events.

Hope that helps.