Positioning is everything, make sure your tanks understand that line of sight is your greatest and weakest strength
Work on your accuracy, sleeping flankers, ults and healers
Don't underestimate an ana on attack, nano boosting characters that don't do much damage but can hit more than one target at a time like winston is actually really useful
Biotic grenade is one of the best abilities in the game making dva and shield tanks your worst enemy
Pro tip: quick scoping is a thing with ana because scoped shots are more accurate than non scoped making it a useful trick for mid range heals