Music theory isn't everything but understanding it will definitely increase your skill level in a number of important areas.
Here's the list along with some related lessons.
1.Harmonise A Scale
This is a key element of music as songs are formed from chord progressions. You will play the chord tones more often than not so knowing harmony and how it relates to a key is essential.
2.Think In Formulas
Musicians often use roman numerals to indicate which chord they're playing. In the long run it's a much easier way of communicating and learning new songs. The blues is a classic I IV V chord progression.
3.Learn the major/relative minor and pentatonics
I cannot stress how much music you can make by knowing this! It takes a while for the light bulb to go off but the major, natural minor, major pentatonic, and minor pentatonic are all basically the same. So much music is based off that stuff...
4.Learn The Dorian & Mixolydian Modes
There are 7 modes in the major scale but these two (along with the Ionian and Aeolian which are the major and minor scales respectively) are found a lot.
Groove is the lifeblood of a bass player. Develop it and you will have immense power...
Rhythm is organised into beats and bars. Time signatures represent the different feels you find in music and to expand your rhythmic knowledge you need to know a few.
7.Know your intervals
Intervals are the distance between two notes and all bass lines are comprised of different ones. This helps your ear to recognise your favourite bass lines as well as give you the ability to instantly create your own.
Another important and extremely common building block of bass lines.
Chords are fun to play on bass and further enhance your harmonic repertoire. Arpeggios are just chords with the notes played separately.
10.Learn The Circle Of 5ths/4ths
This is an extremely powerful way of learning the notes of all 12 major/relative minor keys. Once you know that, you can:
- Read music more easily as you can find the shapes related to the key you're in
- Learn more difficult styles like jazz which often changes keys multiple times in songs
- Sharpen your music theory skills
- Find the modes/triads/arpeggios in a key quickly
- Become more musically literate
There's a lot here but the topics found in this post and on the video lessons will take you a long way to improving your bass playing. Take your time and return to this page often until the information becomes second nature. Remember to always make music with these ideas!