If you want to have a crack at doing things properly, I'd suggest giving reading a go. The simple sight reading for bass by a chap called Josquin De Pres is worth the outlay. I spent a few months on this (30 minutes a day) when I was 18 and it transformed my reading and understanding of music. Took a month or two to get it sorted then just practice.
I then went on and did the grades (myself) which then led me to becoming a professional teacher at a music college (sadly, something I wasn't particularly great at).
At the same time I invested some time in theory and my knowledge of the instrument (intervals, synthetic scales etc.) that helped me get a much better grasp of what I was doing and led me to get some good gigs. At all times it was related back to use in a practical situation.
Then, after being in bands for about 10 years I sort of got bored with it, and then took up other things. Now, I can still read but slowly and my theory is rusty, but it's still there in the recesses of my brain if I need it, and it was an awful lot of fun learning it.
I'd say set your aspirations and create a plan to get there. It's easier said than done because I'm very motivated if I want to achieve something. The next stage for me is mastering DB, which I'm starting now.