For farming energy, you either use the Rein trick to get to ~80% early, or you just let opponent's Roadhog hook people so you can bubble them.

Avoid using your bubble on people that are not commited to a fight. Like people peeking corners. You think that person is going all in and will be shot, but then he strafes back to the wall and you get nothing out of it.

For self bubble, try to use it when you hear the sound of your shield breaking, not before. If you bubble early, people will avoid shooting you and then you will be left with 400HP. If you bubble on critical time, you will get energy, because people are going crazy for the kill, and you end up having 600HP and a chance to outdamage the opponent. This trick wins you 1v1s against Zarya on ecopoint 100% of the times.

Another trick is to use your beam + grenades when you are 1v1ing. This makes you burn their HP faster. It wastes more energy, but it's great for 1v1s, when you dont to give them a chance to run away or get support from another player.

For her positioning. Try to stay between people, not in front of everyone like you would as Rein, 'cause this way you can pay more attention on who to bubble. If you don't see any team mates in front of you, you are most likely going to die.

For ultimate, you don't always need to hit 4+ people. If you lock 2 squishy targets like a Soldier and an Ana and kill them, it's GG, it delays the other team a lot.

If you get a Reinhardt on your Graviton, the most you can do is to jump into it so you can bomb them, or else the shield is just gonna deny all your damage.