I hate practicing. It's boring and hard work and I'm a lazy person. So my goal is to maximize my time - I pick a skill that I can't do that I don't have or haven't been doing well and focus on it until it improves. It sounds overly simple but I think a lot of people overlook the fundamental fact that practicing is not meant to be fun, it's meant to make you a better player.
Time getting ragged? Use your metronome and run scales or excercises until it's tight.
Can't remember the chords to a song? Run through it until your fingers know it better than you do.
Can't quite play a lick cleanly, like in something like Help/Slip? Both of the above techniques come into play... slow it down until you really really understand it rhythmically, this usually finds me starting at about half tempo. Gradually slow it down, patiently making sure you can play it cleanly at each faster click of the metronome, until you can cleanly play it at full speed or faster.
Trouble coming up with enough ideas for something like the opening jam to UJB? I'll go as far as making a chart of all the notes of every chord in the progression, and find ways to connect them melodically.
Of course sometimes I'll noodle around freely on a bass at home too, usually after some

inspiration - this also has benefit, especially if you're adapting to a new instrument. I usually try to free my mind of anything besides "majorish" or "minorish" and play around with different intervals and find ways to express myself harmonically. A lot of my most fundamental techniques have been honed this way.