QP isn't a good practicing ground imo cause you don't understand where to position yourself since everyone is scattered everywhere. Try comp, who cares if you get bronze? You will eventually get better and move up the ranks as you play more and more.
Depends on what hasn't improved. You can improve a lot of you try to counter instead of the normal 6 dps. Game sense is different and better learned in teams. Get a friend or two and try quick play that way and try to play around your team mates picks. Otherwise just pick a char you really enjoy and try your best and hope to add decent team mates