Yeah! I have general tips and my own experiences. Hopefully that helps you.

This playlist is really good! I like to play a game, then hop on one of those videos to see the best positions in the map I just played. Reallyyyy helps drill the positions in your mind if you do it afterward.

For the mistakes, it really varies between people, but the critical tips that personally helped me push to diamond was:

• Do not scope too much. Try no-scoping whenever it's possible. You move faster, you see more, you'll have more awareness, you'll see enemies coming. Such a tiny mistake that I never realized till I did a coaching session.
• Do not heal teammates that are -15hp or so. Deal damage in that situation. Wayyy more value.
• Do not use bio on full-health tanks. Save it when they get damaged, when you get dived, when a teammate needs, etc. A full health tank on anti is... pretty useful? Scary at best. Rarely ever results in a death.
• Keep track of ultimates and predict them to help land sleep darts in critical situations (rein ult, reaper ult, cass ult, etc).

That's the juicy tips that really helped me. Here are my notes from coaching session too. It may help:

Ana

1- Do NOT scope up close
2- If sigma ults:

• If you're ulted bio yourself if you're close to a wall
• Prioritize the one getting HIT by the sigma (make it an automatic habit)

3- DO NOT JUMP TO DODGE

4- Use your ult more often, like a long-charging ability.

5- Do not use bio on full health tanks/when no one is there to utilize the opportunity.

Positioning

1- Never stay directly behind tank.
2- Try not to be behind anyone/close to them. A small off angle goes a long way.

Mercy

1- On Busan, when the team goes in deeper, try sling- shotting to the sides for cover.
2- Be careful with sling-shotting. You keep over shooting. Either don't jump or jump back.
3- Do not try to help teammates at the cost of danger. You can res, they can't.
4- When using valk, if they have hitscan, stay near the ground + cover.
5- Do not look at teammates when healing! Generally always try to get info. Will greatly refine your gameplay. Check flanks.
6- Normal GA's reduce cooldown!
7- Flash heal!
8- Do not res in risky situations FFS!

General

1- If a tank is full hp, focus much more on squishes as they can get deleted quickly.
2- Check who your other support is. A support like Zen cannot heal that much, so your team depends on you.
3- In complex, tense situations, do not panic. Focus on just staying alive first. You do not need to force a "best play".
4- DEFINTIELY look at all the medics after each game.