Sound is also an important aspect of Counterstrike: Source. More than 80% of the players on public server wont sneak around using the shift key. So you will be able to hear them walking almost all the time. I recommend a good headset while playing Counterstrike: Source. When you hear an enemy walking you can predict his position and the route he is taking.This way you can gain a pretty significant advantage, which might be just the thing you need.
This brings us to the other subject you want to master: prediction of the enemy routes and thoughts. If you hear an enemy walking you need to listen carefully to determine which way they are going. This will enable you to predict the path they will take (Most players tend to use the same route often). It requires a bit of knowledge of the routes available on the maps. But if you master this technique you can outsmart your enemy quite easily.
Another thing you should do is to think like your enemy. If you are under fire you need to try figuring out what your enemy is thinking. Now you can try predicting his next move (most of the newer players are easily predictable). For example you can hide around the corner he is heading towards and wait till he approaches you. Then you pop around the corner right before he reaches it. ‘Boom, enemy down!’. This is aneasy way for you to fool your enemy and pretend as if you are retreating. Most enemy’s will follow you straight away and become an easy target for you.