1. Practice your aim. A lot.
2. Sleep dart ults, use for stagger, defense etc.
3. Sleep dart has a weird animation so practice the timing and account for travel time
4. Hip fire is projectile, scope is hitscan. Sometimes you may want hitscan if your team is farther away/helping shoot enemies.
5. Your grenade is often more useful in denying enemies health than extra for your team. Can nullify a zen ult, stop hog heal, etc.
6. Don't stay still. Your hurtbox is weird when moving so it will make you much harder to be shot.
7. You don't have to throw the grenade at your feet/moce to the team to heal them. Learn the lobbing angle so you can hit your team with the grenade from farther away/finish enemies etc
8. If you are dove, hit a sleep, then as soon as the animation ends (there's a sound cue too) you can shoot, nade, shoot + melee
9. Practice reload cancelling. As soon as you have the ammo count change you can melee and start shooting again. Useful for some characters more than others, but as far as I am aware, it is never bad to do.