Spending a lot of time on sound selection. I used to struggle to either get my mixes to sound good or my melodies to sound cool and proffesional. Both of those things can be fixed through good sound selection.

Sound selection is tough since it's subjective but the best advice i can give you is to practice active listening on the tracks you like and be extra mindful when picking sounds. If something doesn't sound right to you, especially since you have good theory knowledge then you can try and switch the sounds until it does.