There's lots of good material and advice here. I would suggest that as you learn different things, scales, chords, modes, whatever, that you immediately apply it to your bass. Once you play what you have learned, create a piece of music using that idea. It doesn't have to be great.... it doesn't even have to be good enough to share with anyone, but try to use the knowledge in a musical way. Make the theory lessons work for you, don't just memorize information and hope that you'll see how it applies later.
Never confuse beauty with things that put your mind at ease. -Charles E. Ives