A few weeks ago, I published a bass guitar exercise that I've used for 30 years. It's no exaggeration to say that this single exercise has done more for my understanding of music theory, analysing bass lines, and writing my own than almost any other single thing I've learned.
It took Nancy - one of my subscribers - to remind me that, actually I add two more elements to that exercise in order to create one super-monstrous bass exercise.
Here it is...
Essentially, you take a G Major scale (although do move it to different keys and strings) and play the following on each degree of the scale:
With all that information, you can start to create bass lines, strengthen your ear (since bass lines are made up from these component music-theoretical parts), and work on your technique.
Take this in any direction you so wish!
Scroll down for the free PDF. It's a bit of a behemoth of an exercise and there's a lot to learn. But, you will be richly rewarded with new bass skills should you choose to tackle it.