grade A advice here,
Your first 2 shots are going to be accurate if you're standing still, if you're not standing still only your first shot will be accurate.
So it's better to shoot when you are in a still position, but this also makes you an easier target, so you have to learn how to take a couple of shots then quickly strafe and come to a sharp stop and take some more.
However, if you're at a close distance no amount of strafing is going to save you, so here's what you do.
You aim your first 3 shots at your opponents head, then you drag down the cursor to the middle of his stomache, the recoil will either give you more head shots or light his chest on fire, which is both acceptable.
Keep in mind you want to be a moving target.
Pro players can feel the rythmn of an opponents fire and will do his/her best to time attacking and defensive maneuvers accordingly. Strafing parallel to your opponent will make you a difficult target to hit, so you want to keep that in mind to. You want to take corners at an angle that makes you parallel to any wood be opponents shooting at you.
If you need practice aiming, use a USP only and aim only for the head. You will die lots! But the practice is good.
As for camping around corners, try to find textures on the walls or objects that are the same height of your opponent's head. And also lead off away from the corner the amount of space you think is necessary to time a head shot, this all has to do with reflexes. If you have a 1.5 second reaction time, try to imagine how far the opponent will get if he/she came around the corner at full speed, then place your cursor there at head level, and the do the 2/3 shots to the head then drag down technique.
Hope this helps. -Dan