if you are coming from lead guitar world i would recommend focusing just on the groove and not doing fills for a while. work on your time and your rhythmic skills and lastly locking with the drummer. this is a support instrument (in most cases) and making the rhythm section a cohesive unit is more important than cool sounding fills.
this might take a while, that's ok. once you have the foundation, then you can start adding some fills back, just one every 4 measures max to start, and go from there. you will find that with interesting enough basslines fills aren't need, for instance Marvin Gaye's What's Going On has so much going on that you don't need to fill, the line themselves are so fun with lots of movement. most good basslines will be like that, just fun to play (come together by beatles another one that's simple but just fun, no fills needed).