1 Learn what's threatening and what's not. General rule of defense is to learn what is a threat and what's not. opponents facing your net with a dribble at quarter field. Threatening. They are facing the corner, not threatening, just lookout for a pass. If there isn't an immediate threat get in a good position and either force a touch or challenge.
2 Teammate rotating back while you are in a 1v1? Challenge when optimal, but delay the play as far as you can before it becomes too threatening then make a save. This gives your teammate time to get in a good spot for a potential clear or save later on.
3 The ball doesn't always have to be in the opponents half. If you are last back and if the opponent gains possession and you'll be in a 1v1, touch the ball to your own corner and buy time for teammates to get in a more comfortable position to challenge or clear the ball.
4 If you make a play attempt and your play is almost over but you can squeeze in 1 more 50/50... DONT. This causes confusion with your teammates and causes them to be out of an optimal position to make a play as you added another layer of uncertainty. Your not in comms or a pro so just don't.
5 Force a play. You are first man on defense with your teammate(s) covering net? Challenge or fake challenge depending on situation. This will force your opponent to flick or hit the ball away giving free possession to your teammate.
6 Read the play. Stop watching the ball when not on it and watch your teammates and opponents. Learn the patterns of where the ball will go in case of 1.) dunk 2.) 50/50 3.) a beat. Look at the ball just to see the current direction it is heading then look at the upcoming challenge, place yourself where you can cover all possibilities. (this takes ALOT of time to learn)
7 Possible opponent clear? Stay farther back. Many people learn how to hit the ball hard early on, if your too close you'll be out of position. If you are farther back and they hard clear you have free possession. But don't just bail out because the opponent may see that and decide to control it. Just keep your distance.
8 Don't all in challenge all the time. All in challenges are where your teammate just set up a play but they wont recover quickly so if you go, you could possibly score or, if you whiff, get 50/50d, or make a bad touch, you get scored on. Remember winning isn't about scoring all the time, if your opponent cant score, all you need is 1 goal to win.
9 Stop boosting and flipping so much. The faster you go the harder to read a play. Slow down unless needed to beat an opponent , get a shot or to reposition on defense. The more boost you hold the easier to get a beat around the opponents. If you constantly flip your forced to go in a certain direction. Flip only when the ball wont change directions. If you flip and the ball goes in a different direction than you anticipated, you are overcommitted leading to a bad touch or being out of the play.
10 Cover area on the field. Read where the field is not covered and cover it. In the current meta for 3v3 rotations aren't just 1st man 2nd man 3rd man, at higher level play its about coverage. You still follow basic principles but 2nd man and 3rd man can swap just by how the ball is hit. if you are second man cover the area where you predict the ball to go for a possible shot, if you are 3rd man cover where your second man isn't and be farther back just in case of a hard clear