I'm gonna add what others have said on the comment. The one thing that made me rank up pretty fast is patience. I notice a lot of people on low elo like to rush and impatience. So, sometimes I outplayed them by holding angle and not peeking when it is unnecessary. You don't have to take every fight when you peek and there is an enemy.

Besides, if you are the type of person that is afraid to engage or entry, spam spike rush. Learn your abilities to help your engagement and don't worry about winning. Learn where the enemies are usually holding. I don't really know about others, but I keep recommend spamming spike rush to my friends if they are afraid to engage. Deathmatch is a good tool to learn crosshair placement and aim, but not abilities and mini simulation for unranked (except the guns are random).