You have partly answered your own question. Practise the things you have trouble with.
Break things down into manageable chunks. When I was younger, CD machines had a way to keep repeating passages (the button said A-B or something). If your CD or MP3 player can do this, you can practise keeping time with short, easily remembered bits instead of having to stress about remembering the whole song. If your device can slow it down, all the better.
I'm not sure what you understand by theory, but what you said there is music theory. Theory is just a way to communicate music to other people without actually using music, e.g. if you're in Starbucks without your instrument talking to another musician you can quickly say "It's a simple I-IV-V" without having to explain where your fingers go on the fretboard and so on. To learn theory it might be better to look at piano or guitar based resources, because they are more likely to get quickly to relationships between chords and scales.
The important thing is to know what you are hearing. Listen to music that gives you chills, goosebumps, a happy smile, makes you think of waterfalls or whatever. Listen to the bass line without touching your bass and learn to sing it. Once it is locked into your brain, pick up your bass and play the notes that you sing. Then identify what the notes are and what the intervals are between them. Learn to play exactly the same thing in different places up and down the neck. When you can do this with about 20 tunes, you will be in a good place to start studying theory, because then you will have a better idea of what theory is trying to explain.
i struggle to keep time while playing
Break things down into manageable chunks. When I was younger, CD machines had a way to keep repeating passages (the button said A-B or something). If your CD or MP3 player can do this, you can practise keeping time with short, easily remembered bits instead of having to stress about remembering the whole song. If your device can slow it down, all the better.
I would really like somewhere that explains what notes are used in common keys and why and how to know what notes work together with chords
I'm not sure what you understand by theory, but what you said there is music theory. Theory is just a way to communicate music to other people without actually using music, e.g. if you're in Starbucks without your instrument talking to another musician you can quickly say "It's a simple I-IV-V" without having to explain where your fingers go on the fretboard and so on. To learn theory it might be better to look at piano or guitar based resources, because they are more likely to get quickly to relationships between chords and scales.
The important thing is to know what you are hearing. Listen to music that gives you chills, goosebumps, a happy smile, makes you think of waterfalls or whatever. Listen to the bass line without touching your bass and learn to sing it. Once it is locked into your brain, pick up your bass and play the notes that you sing. Then identify what the notes are and what the intervals are between them. Learn to play exactly the same thing in different places up and down the neck. When you can do this with about 20 tunes, you will be in a good place to start studying theory, because then you will have a better idea of what theory is trying to explain.
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