Download a map from the workshop named AIM BOTZ ove of the ebst aim maps, aswell if you want to practice reflex you have to install training_aim_csgo2 its most used to reflex either tho its named aim map i used it before to train my reflexes so yeah
EDIT: Aswell you can watch some pro matches and matches of other people to check how they play
1. Don't use P90 all the time, although it's easy to use, it won't get you used to higher recoil guns like the AK-47.
2. Study the recoil patterns of the AK and the M4A4 / M4A1 - S as they are the most popular guns, and you'll be using these most of your time in CounterStrike. Also, you could practice one taps with the AK, just try and go for 1 shot headshots at longer range in deathmatch for a little while till you think you get used to it.
3. Walk around, with your crosshair at head height. When moving around, your crosshair should be placed at where-ever an enemy could come from, and where their head would be. For example, whilst clearing out a bomb site, you should be checking corners, windows, doorways, anywhere an enemy could be hiding, and aiming for where their head could be.
4. Eco rounds, are rounds where you don't buy any weapons, armour or equipment. Maybe a P250 or somesort of other armour-piercing pistol. You do an Eco round usually after you lose the first round of a half. Reason for doing these is because you don't have much money across your entire team, so doing an Eco round will gain more money for your team, even if you lose.
I think these are some of the more useful tips for a new CS player.