Little diatonic (notes of the scale) or chromatic (notes in fret order) as fills do sound good if used correctly.
To pull this off we need to see how much space will the song let us have for our run? Two beats, three beats, four beats, etc. Fill it with a diatonic or chromatic run.
Country uses this to call attention to the next chord change. When the guys hear the run they know a new chord is coming up. The Country bassist will leave early and time their run so they land on the next root
at the chord change. Check out 1:02 to 1:30 of this video:
https://www.google.com/?gws_rd=ssl#q=scott groves, country bass
I have good luck using a run at the end of a verse, using it as a walk to the next verse. You have to have some space and if the song gives you that space, fill it with a run. Be aware nothing worst than being half way in your run and someone else takes off on
his run or the vocalist starts the new verse in the middle of your run to that verse. Best to work all this out before hand.
Good luck.
Just found this, probably worth your time. Takes Scott till about 5:00 in the video to get into what I'd like you to hear.
Target (find) where you want to be next, then walk to it in the space (time) allowed, they all will be passing notes so
just about anything you use will sound good. IMO your ear will tell you what is needed. Willie's walk on this video is E, F, F#, G# then A that's not diatonic or chromatic it's just a walk that sounds good. Point of interest; song in 4/4 time and his walk is 4 notes then lands on the next chord for the first beat of the new chord. Any walk is dictated by the time the song gives for that walk. Got two beats; use a two beat walk.