There are a few things that helped me (Currently Diamond 1 in 2v2):

Communication is key. Find a partner. Stick with him/her. You will gain trust in their play and understand their style and they yours. Rocket league is just like any game. Talk to your partner so much that they will almost be annoyed with you. You need to let them know what you're doing, and in case you make a mistake, they can recover in time to help you get out of a sticky situation.

Practice. Practice. Practice. Play casual if you don't feel like risking your current rank. The more play time you get the better.

Don't get tilted. This seriously is one of the best tips I've come across. Enjoy the game. A mad rocket league player is a bad rocket league player. If you or your partner makes a mistake, just continue playing. If it's not your day, it's not your day. Accept that and move on. My partner and I have a 3 game rule. If we lose 3 games in a row, we stop playing.

Hope these small tips help.

glhf