Here are three simple tips that can help you get better at becoming a professional in the Counter Strike Global Offensive..
Use cover effectively: There are a number of boxes, crates and obstacles around the CSGO maps that you can make use of in order to make you a difficult target to hit. Although, it's important for you to ensure that your cover isn't easy to get perforated with normal gun fire, as this will make your cover totally useless.
Crouch when shooting: Another thing that I've found exceptionally helpful when trying to chase an enemy, is to bend a bit, when shooting. This may possibly result in the bullet spread of your weapon to decrease enormously, which means that you are able to get more shots toward your enemies.
Have Quick Reflexes: This game is really fast paced and based on 1v1 gun fights many times; so it's important that you shot at first prior to your enemies do it. That said, before you see an enemy on your screen, start firing before it's fully targeted in your head.
And that's it! Hopefully, the above mentioned points will certainly help you move ahead faster in the game and level up quick. Feel free to post your queries in the comments.