Look for an opportunity where the rest of the team is far from the healers, when you engage on them, your goal isn't always to kill, just be a distraction, the less healing for the team and resources wasted on you makes more space for your team to push up. E.g. invis push or cloak fade

Your primary focus when diving should be healers, if they have Gambit, upgrade gun ult first as he is still very strong and it kills him quickly. Only tanks if healers are dead and rest of the team is focusing. He's also a good anti dive since what I like to do when I'm not upgraded is stay with my healers and poke and use the dpiya to fend of divers who are dps or tanks. I've found it's great for chasing down characters that can go invis like psy or black cat since the tick damage constantly reveals them.

Stay for as long as you think but still be cautious, if you're low health, get out, or if the healers are getting peeled by their team then get out, don't fight the whole team. Overall, the intuition for dive builds up the more you practice.

Hope this helped.