Advice for improvement?

Hi all! I just downloaded Overwatch on pc. I used to play Overwatch 1 when it first came out, on Xbox. But quit when covid happened. I used to main as Sombra, Lucio, Mercy, Dva or Bastion. Now I’m playing again and would really like to get better especially for competitive, but I have no idea where to start.

Any advice/tips would be greatly appreciated!