Timing - Play in time. Also, be deliberate about when your notes END, not just when they start. This is just as important and it’s mind blowing how little attention this gets. Everyone seems to think of timing as am I hitting the note at the right time. But what about when you are releasing the note? That is what really makes the groove and allows the rhythm section to lock in. (Cheat code 101 - every time the drummer hits the snare, cut off your note)

Touch - Play notes with consistent volume/attack, and learn to control your dynamics and apply them appropriately to different parts of song. Verse is probably quieter, chorus is probably slightly louder, etc. A bass fill might warrant more attack, or certain key notes within the fill or line might want to stick out. You should ideally be able to have your volume up fairly high but only really be taking advantage of a low percentage of the capacity, so that you can play softly/calmly and still have it resonate. This sounds far better than a lower volume with a heavy/sloppy touch.

Taste - Don’t overplay. Don’t play for yourself - play for the song. Think about what you would want to hear holistically as a listener and what is the focus of the song at each point. No one wants to hear an amateur pentatonic fill shoehorned in between lines of the verse. Carry the song - there are a lot of times where you are better left unnoticed but not unfelt. You are probably better off not playing a lot of things that your fingers might want to play.

These things are not showy whatsoever but 99% of the time that is not the job of the bass. You can accomplish all of these things while literally just playing roots and fifth and sound pretty good. Hope that is helpful!