I’m compiling notes from hero guides to a general guide with each hero. What are common mistakes on your hero?
For d.va, it is using matrix too long for things that only need a short flash. Also immediately matrixing an ulting mccree, when he won’t shoot in that first half second. Save matrix, and use it once he’s has significant dmg locked on.
When playing Lucio and using beat don’t jump up in the air and do it because it takes longer.
Playing him, hoping to win.
Sombra: Thinking that landing hack is value in itself.
Mei: Thinking that the freezygun is what makes you strong.
Sombra: Stealth is a noob trap, if you’re constantly staying in it for more than ten seconds, you’re practically afk.
Mei: Don’t forget about the icewall you put down. Break the icewall when you no longer need it or when it becomes a detriment to your team. Especially when you have a hammond on your team.
Icewall is a powerful and versatile ability, but it also gets your teammates killed if you don’t manage it properly. You start running into problems quickly when you don’t track who’s on either side.
Zenyatta: They tend to forget they have healing orbs. Zen is probably the most consistent healer in the game, he’s the best healer if you’re on a high mobility team if don’t forget that you cn juggle both discord AND harmony orbs mid fight.
Orisa: They play her like Reinhardt. Rather than planning ahead and placing a shield where it’s needed, they put it down at their feet in reaction to the moment instead, which ends up rooting them in one spot while the rest of the team moves on. Dude, go play Reinhardt.
For heroes I play often:
Mercy: Not canceling GA and going too far into enemies
Genji: Wasting swift strike before ulting
D.va: Same as you said, but I’d say also going too high with the self destruct and killing nobody. I’ve done this so many times when it would have been useful. 
Widowmaker: Being too stressed out, trying to relax has helped me hit shots way better, also turn off team chat 
Reaper: Needlessly using his escape ability
bastion will survive longer by constantly going in and out of sentry mode and using headglitches whilst in turret mode helps survival a lot
As Moira, using Coalescence when I’m about to die ;-;
Reinhardt: Turtling. Like… MOVE! THEY DON’T EVEN HAVE A MEI! JUST PRESS W FOR GOD SAKE.
Roadhog: Most guy would just feed on him then whine about nothing is being done. Like, we could have done something if their Zarya hasn’t gotten her third graviton while our supports haven’t got their ults yet.
Doomfist: Try playing him like how the forum described him and then I wonder why they have sub 0.5 kda