Brush up on your scales & arpeggios. (In all 12 keys) Including the: Major/Natural Minor, Pentatonic Major/Minor, Melodic & Harmonic minor as well. Then when you have those down practice the scales modally. EX: G dorian mode, mixolydian mode, etc. melodic/harmonic minor, and pent major/minor, because a few of my students who have a good grasp of the major and minor scales in Ionian mode dont know the others)
This will give you a very firm grasp as to what your note choices are for any given chord changes.
Also listen to every type of music out there. Dont like Jazz, listen to it anyway. Jazz is an excellent sourse for listening to improv. By listening to the other styles of music you are going to open yourself up to new ideas for bass lines that you might never thought of doing. In short, it will expand your creativity.