I've been a heavy FPS player my whole life. Counter Strike: Source, the precursor of CS:GO, was one of my favorite games to play when I was bored. Naturally, I took up CS:GO as soon as I had the money to buy it. Learning a new shooter is generally rough. One has to get used to the different sensitivities and new mechanics. It is only through vigorous trial and error that one can finely tune their specifications optimally.
In CS:GO, there are a handful of "roles" based on mindset and weapon choice. The two roles I favor are the "AWPer" and the "Shot-caller". The AWPer role is named after the infamous AWP sniper rifle. AWPs are unique in that they are a one shot kill anywhere on the body except for the legs. Thus, AWPers are those who specialize in using the deadly weapon in all situations. Shot-callers are effectively the ones who tell the team what they are doing. Weapon choice doesn't matter too much, but rifles are generally used. When I am shot-calling (Generally because no one else is doing it), I tend to play more aggressively and use radical tactics, while as an AWPer I patient and methodical.
For those with an interest in FPS games, CS:GO is one you should definitely try out.
Here is a guide useful for any player, new or experienced.