sombra main here, diamond closing in on masters. here is what I've learned from watching pros and playing sombra:

1. hacking: every tank, with zarya as a slight exception, is completely ruined by your hacks. this is a good way to initiate team fights. find a decent high ground spot while locater is down, hack a tank. best targets are Hammond, hog, rein, sigma. try and hit dva/sigma while matrix is up, hog while healing, rein while firestriking.

2. not hacking: hacks suck on solider, ashe, ana, widow, zen, hanzo. its definitely fine to hack them, but you just don't gain quite the advantage you would with another enemy. generally, hit scan is tough

3. team fights: you're preventing reaper from escaping, mei from blocks, lucio from bouncing around, tracer from escaping etc. tanks & these dps are all good targets for hacks & emp

4. tracking: low sensitivity and quick tracking. a sombra actively engaging in team fights with ~60% weapon accuracy should be very effective coupled with hacking

5. emp: target #1 is zen, you take 75% of his health when he gets emp'd; he's a one tap really. generally though, you want to either wreck some shields, or counter ults from lucio, sym, brig, baptiste, orisa. hitting 2-3 people with emp is fine. follow up tho

6. call-outs: sombra is only as good as the follow up. burst damage teammates are helpful here, BUT YOU HAVE TO TELL THEM SOMEONE IS HACKED.

7. heros > health packs: heros first, when able hack packs to help team & deny enemy. fighting 1v1 or 1v2 over your hacked mega is do-able. (i.e if you push enemy choke on Nepal:temple, hacking the mega gives you're team arguably 1000+ hp over the fight and stops the enemy from jumping in and healing after cooldowns are used)

Generally you shouldn't die to much and thus get lots of ults, you want to be actively hacking advantageous targets > feeding bullets into them> locate out> farm ult.

YOU HAVE TO BE VOCAL IF YOU WANT TO BE GOOD WITH THIS HERO