Just play some casual/team deathmatch. If you care about ranking up don't go on competitive right away. Practice a lot, get used to aiming, find guns you like to use. Overall just learn more about the game.

A great way to get better, is learn and understand the game. You need to understand how the mechanics work, such as recoil. Now, there are plenty of videos on YouTube that will help you out, best thing to do is play the game though. CS is a game that you get better at overtime (for most people that is).

TIPS

Crosshair Placement - Place your crosshair at head level and pre aim to where you think enemies might be

Movement - Movement will come to you overtime mainly, but don't walk around like a bot everywhere.

Game Sense - Know the map and your surroundings, be aware of what is going on.

Teamwork - CS is a game that you must use teamwork in. Communicate and help out others, don't go run into a site by yourself.

Of course there are much more things to the game, but work on these and it will help you out greatly. As someone already suggested, play Deathmatch frequently.