Start with something simple that you can play without any real effort. This gets your mind in gear with sounds and bass.
Then move to something that has been difficult for you in a past gig or rehearsal. Not necessarily a whole song, just fill or something that didn't get played smoothly.
After that, do something that this not on your 'playlist'. Like new kinds of scale forms, chords, songs you've heard on the TV or from some place that has nothing to do with bass. For instance, folk songs, children's songs, a song you knew in HS, or something classical.
Lastly, play something that makes you feel good as a bassist.
Don't just fluff through these things, take time to get them right.
Never confuse beauty with things that put your mind at ease. -Charles E. Ives