I'm not a genius in improvising as well, but I do think I can give some advice.
At first, pentatonics [i]are[/i] a good start. You can play a lot of really great stuff with only pentatonics.
The best tip I can think off: try to learn several different styles. Take a few weeks to focus on one genre, like blues, for example, and learn all about it. Do some research and look for interesting bassplayers (wikipedia, deezer and youtube are great resources) and don't forget the basic stuff. After a while, you'll start implementing stuff you've learned into your playing [i]and[/i] your improvising.
Learning different scales is great stuff too. The dorian mode (minor scale with a major sixth), for example, is a great alternative scale for improvising when playing in minor.
There is one thing, or at least so I think, that you shouldn't forget: don't show off (too much) with technical skills. 'Cause sometimes less is more.