One thing to do with Torbjorn is to always have a turret down. The level 1 costs nothing and can do a decent amount of damage. Try and place it in an area where it can only be accessed from behind by your team or put it somewhere that it is somewhat protected.
Leveling it to level 2 takes 6 hits from your hammer. I would put one down at the start of the map and level it up and then leave it. Your main gun does solid damage (the projectile arcs at range) and the right-click is a spread for close up. The spread does pretty well at covering doors and can take out Tracer.
I would work at bothering the other team with my teammates and having the turret provide support from afar. I would never repair it unless there wasn't an active firefight. Sometimes I would swing by and kill the person attacking it because they focus on it and not you.
Your Q gives you like 500 armor and makes you stronger. It also temporarily makes your turret level 3 that shoots rockets as well. I have used it to get a couple triple kills and one quad kill. Got a play of the game due to it (and turret wasn't even involved in that one).
Also every time someone dies they drop scraps, when you get 50 scraps you can give out armor packs. Always make sure you have armor on and then throw out armor packs for your teammates to pick up.
Edit: also don't be Torbjorn on attack. If your team is pushing properly, the field moves too much and your turret will become useless.
Thanks.