You can't exactly place down tactics and strategies coz u will learn as you go but these are mine in general...
1) with the crosshair there is a "t" the t should be a tad bit above the enemies head to get a head shot
2) take time to aim and fire, don't go ballistic as soon as u seen someone coz chances are thay they end up killing u before u can
3) try to walk if you can, walking doesn't create any footstep sounds so the enemy can't detect where u are...
4) guns such as the ak-47 have massive recoil and will only work well by using "burst fire" that is firing in burst rounds, or "tap fire" just tap on you mouse in bursts of 1 sec or 3 bullets... with the ak, u can aim at the neck, the kick in the ak will do the rest
5) crouch when u shoot, its increases the accuracy
6) there will be times when u play and u hear terms such as "gay awper" or "awper fags". The awp is a short term for "artic warfare precision" rifle. It is a sniper rifle and very very powerful. Basically a one shot kill weapon, providing if the shot is well placed enough... but then always try and crouch as well when u shoot from the awp. it improves on accuracy
7) on the ct's, the most common and best gun/rifle u will use will be the colt, or b43. That gun is by far the most accurate and iis comparable to the ak47. the ak is more powerful but less accurate and will have to take time to master. The colt has a silencer to put on, usually clicking on the right mouse button. Without the silence, the colt is more powerful but less accurate. Will the silencer on, its less powerful but more accurate. Its an accepted fact. Unlike the ak, the recoil goes from side to side, not up.
8) When you play, you might get shot from somone even though u haven't seen them yet. They might be shooting through the wall. this is possble though not all walls be be shot through. Brick walls, wooden crates and doors can be easily penitrated so don't say "hack or cheat" coz they can be
9) early in the game where u wouldn't have enough money yet to buy a good guy, a good pistol should usually do the trick. the desert eagle is by the most effective and powerful but holds the least amount of rounds of all the pistols. 7 rounds per fire. The USP pistol, the gun te ct's start off with is by far the most effective with a silencer included, though as mentioned, the desert eagle is by far the most powerful to use when you are strapped of cash to buy a newer gun.
10) after the first or second round. you would usually have enough money to get an mp5. a submachine gun with fairly good accuracy even on full auto and if aimed correctly, headshots are fairly easy. if u are strapped with cash, the mp5 is the best gun to buy and use
11) when sniping, try to get a sidearm pistol, notable the desert eagle coz that gun will prove very handy during close quarter battles
12) being a n00b, u should try everything to improve your aim. Camping is once such idead where u stay in the same spot for over a period of tiem, but this does not allow you to know the map well or get any aim practice. camping for n00bs will only provide aiming skills such that, they know where the head will be when the enemy walks around.. so its not that bad... but camping is more or less a no-no if u wanna do good.
13) in maps where there are "de" in the name, this means demolition in which the t's have to plant a bomb at a specific site. the ct's have to coutner them. generally, if u are ct u camp at spots until the t's come... that's the idea
14) in hostage rescue maps, its vice versa and terrorists get to camp. one more is assasination maps where the VIP will have to make thier way to some safe haven before that team wins. generally its the ct's./
15) there are also maps that have "fy_iceworld or aim" in them. these are generally considered fun maps and don't follow a set of rules. the aim maps are for aiming and the fy stands for free range I guess, correct me if I'm wrong.
I think that's all u need to know in the mean time, though I can type some more if ur unclear! let me know!