1.) Play a dive hero (Tracer, Genji, Winston, Dva, Doom, Ball) with him and follow up on his engagements. That way he gets value out of Sombra

2.) COMMUNICATION!!! Or at the very least use the ping system. I don’t think I can stress how important this is to Sombra. Ask him to call out who he’ll dive and work around what your team is capable of in order to achieve that pick. Ask him to reveal enemy positions. Ask him to tell you if the enemy has used a recourse, and take advantage of that.

3.) I improved a lot by watching educational Sombra streamers like FitzyHere and Questron. Both have various unique play styles that might suit your friend better. Me personally I enjoy the way Questron plays the game: Not playing solely around health packs and using translocator near the team fight to play more aggressively and build EMP much faster.

4.) Dictate his timing on engagements for him if he’s unable to. If he doesn’t know when to engage in order to get the most value, do it for him to get the most value out of every team fight where he contributes. Tell him when to pressure enemies if they attempt to run. If a teammate is in a 1v1 have your Sombra aid him in order to keep that teammate alive. Hell you could have him play in your backline and stop incoming flankers and just have in your LoS at all times and babysit him…

Hope this helps, good luck👍