I played electric bass when I was in high school and for a time after graduation. I put myself on a long hiatus to finish college, build a career and raise a family. Then about three years ago, when I was making good money, I ordered a Fender Mustang bass guitar and a Fender bass amplifier. I converted my upstairs home office to a music room and began practicing scales and studying music theory.
Playing scales every day, in every key, both major and minor, really worked. I soon knew my bass neck better I ever had, and could hear chord changes much better too. If you really want to play bass, practice scales until your fingers fall off. Yes, it's boring in a way, but so is weight lifting. If you want big muscles, two things are required: (1) effort and (2) patience. It works the same with learning bass. Playing scales is a form of exercise: you are exercising your ears, your fingers and your brain.
Last January (in 2009) I contacted a band advertising for a bass player on Craig's List, and tried out. They liked me, I liked them. We began a steady regimen of weekly practice together, gigging occasionally for mostly unpaid charity events. Meanwhile, my knowledge of bass and bass lines grew exponentially, my ear continued to develop and my confidence grew.
If possible, listen to the videos and recordings with head phones, unless you have larger speakers attached to your computer. The small, built-in speakers in most computers cannot reproduce the bass or the warmth of the original recordings.
I play bass guitar and string bass in and around Hollister, California.