+1 to kraigo. Its useful to free your rhythmic thinking from an instrument and just use your imagination.
Try sticking to the root note to free up the brain space for rhythmic ideas.
Learning notation can go a long way towards increasing your rhythmic awareness. It really pays to internalize how a bass line relates to the metronome pulse.
there are a few books that contain decent catalogs of bass rhythms in various styles.
Bass Bible by Paul Westwood I own and reccommend.
BASS GROOVES: THE ULTIMATE COLLECTION by fellow TB'r Jon Liebman is on my wishlist.
And of course, listening and copying others is invaluable.