I'm an intermediate bass guitarist, and I want to improve my left arm fingers work, and improvisation during bass solo.
I think I should learn not only by simply remember some tabs by famous bass guitarists, but from some excersises.
I advise you to watch video school John Patitucci "Electric Bass". John shows a lot of exercises for the left and right hands. You can find it here http://www.kat.ph/john-patitucci-electric-bass-2-video-pdf-t2949084.html
Also, I recommend you a series of lessons Jamey Aebersold "Play-A-Long". This will help you understand improvisation. http://extratorrent.com/torrent/246065/Aebersold+Jazz+Play-A-Long+Vol.++1+to+Vol.++106.html
Check out Scott's Bass Lessons https://www.scottsbasslessons.com/.
He creates educational videos for all abilities. Most of his videos are free but he also has a paid for area with access to more resources.
I have created as site that has a ton of stuff - arpeggio exercises, transcriptions, a thing called the Pentatonic Lick Factory and lots of other bass guitar related things. There are plenty of things that will challenge even an experienced player.
I play guitar, not bass, but I can answer for the effectiveness of a set of daily exercises for both technique (strength, speed, accuracy) and musical knowledge.
The exercises I use are those in David Mead's book "10 Minute Guitar Workout", but I'm sure others are available. The exercises work to educate your ear as well as your fingers.
Unfortunately, I don't know of a bass version, or an online version.