how do you get better in games

Play them on the hardest difficulty. You'll learn the game in order to beat it. If it's multiplayer, play with people who are better than you or watch their streams. See what they're doing to get tips and ideas. Of course, youtube videos may also have tips and tricks. I say all this, but no matter who I play or who I watch, I''ll never be good at Rocket League. Sigh.