The best way to improve in Skywars is to play and play.
If you are not that good at pvp, I would recommend you to daily practice your skills duelling people, a perfect way to do so is by doing 1v1 duels.
On the other hand, if you are not that skilled in building, you should try to practice your building skills in a single world, as it will be the best way to improve at it.
That being said, you should practice, play, have patience, improve, etc... Dedication is the only thing that matters here. If you don't put enough dedication, 15-30 minutes everyday for example, you won't get better at the game.
With a lot of training and patience, I am sure you'll achieve something. Never give up...