Aiming, shooting and taking cover is what CSS is about. Aim, shoot, cover, make sure you memorize those three keywords because they play the most important roles in Counterstrike: Source. First you need to aim, ofcourse.
And if you think you got your corsshair right, then you should pull the trigger. After you’ve fired your shots you should search for cover.
This is an easy tactic and it works fine most of the times. Every weapon has a certain amount of recoil and weight. This will affect the way the weapon handles and the purposes it can fulfil. If you are entering close combat then your best bet is a shotgun. Shotguns are perfect for doing a massive amount of damage in close combat. Submachine guns also pack quite a punch, they have a large firing rate. The downside of the quick firing rate is that you will be out of ammo in no time. When entering a (very-)close combat situation you should ‘spray’ as much bullets as you can. Also try aiming for the head since that can make a huge difference during close combat. If you are at a medium range an AK or a Colt will prove to be your best companion. The trick is to fire using burst (2-4 bullets) shots. The next thing to do is aiming for his chest, because if you miss his chest there always is a chance that the bullets will go up trough his head. If you are a more experienced player then you might want to aim for the head right away. At long ranges you should use a sniper rifle, either the infamous AWP (Artic Warfare Magnum) or the Scout. The AWP does a lot of damage but takes long to reload. The Scout is weaker then the AWP but reloads much faster. Please note that the AWP is a heavy duty weapon, therefore running with the AWP goes much slower than running with the Scout. You can also use a so called ‘Auto-Sniper’, they are less accurate then a normal sniper but they do not have to reload after every shot.