For me, I would try to get as much kills in pistol rounds.
Then if I win pistol rounds, I get SMGs and try to farm kills to get money. If I lose pistol rounds, I either full eco or get a pistol ONLY.
I also need to anticipate what buy the enemy is having based on how the games are going so far. If I know that they are full eco or weak buy(SMGs or galil/FAMAS), I must get the kelvar+ helmet. If they are doing full buy, I can afford to forgo the helmet.
There are times where I have $5400 and I just buy AWP and Kelvar only.
This one is the most important thing. Dont depend entirety on AWP to get kills. You need to be good at rifling otherwise you will be a liability if you dont have the AWP.