If I had to pick only one scale to play for the rest of my life it would be the major pentatonic scale. Okay, that's cheating a bit as, by learning that scale, I also get to play the minor pentatonic scale (which is related). SO much music is made from the five notes that make up a pentatonic scale. You could write hours and hours of bass lines with it and not get bored.
This video goes in detail into how you can create great lines, solos, and fills with this wonderful scale.
Make sure you check out the lesson on the minor pentatonic too.
Major Pentatonic Shapes For Bass
Learn these shapes across the neck for C Major Pentatonic.

Look at how A Minor Pentatonic is exactly the same shape:

This is why C Major and A Minor are 'related' - they contain the same notes. So learning a major pentatonic scale is two-for-the-price-of-one, making your life easier!
Download the two shapes below.
Here's the backing track used in the video and chord progression below it.
Chord Progression
The backing track uses these chords:

Go through the video and use the backing track with the new shapes you've learnt to make up some lines, fills, and solos. Have fun and revel in the magical power of this cool scale!