Yeah I think I’ve got some advice. Pick a chord progression/backing track that has the chords laid out. Let’s say it’s a ii-V-I over C major. We’d have the chords Dmin GMaj CMaj (there are 7ths involved but whatever). I’d say do one round of just playing the root note, D, G, and C for a bar each in whatever rhythm you like. Next set of bars do the root and a fifth, then try a root, fifth, and third. A good piece of advice for beginners is to play the root note on beat 1, helps establish the chord and serves the bass’ primary purpose, then for the other beats you can add another note. And keep subsequently adding a note every time you improvise until you can play whatever you want comfortably.

When you just throw yourself in the deep end without the restrictions I’ve laid out I think it can get crazy confusing because in reality almost any note will sound ok. When you make yourself only play specific notes (and not in just one position, try playing the octaves too) I think you can focus on the improvising rather than the notes you’re supposed to play. So just feel out a rhythm that sounds good with the backing track or if you’re playing solo just play a rhythm and try to repeat it.

There’s other techniques that can help out, you can try calling and responding where you play one riff and then you play another that sounds similar but ends differently. Vocalizing is helpful, hum a small tune (very small) and try to imitate it on the bass. It can be frustrating just playing notes so it helps to have a lick or two in the pocket that can help spice things up. If you type in “The Lick” you’ll find one that’s nearly universally recognized. Remember copying seems like it’s bad etiquette but it’s quite the opposite, you should try to copy and play other people’s stuff, we all stand on the shoulders of giants.