When I was almost 9, my friend wanted me to join his band. He didn’t ask if I could play anything so he just assumed I played bass since he played guitar. So to impress my friend. I had played Violin for 4 years so I understood notes and had a musical backround. So I looked around in my father’s music room and found a big yellow bass. So I started to teach myself simple songs like 99 red balloons and even made my own tunes. In a year I was able to play more complicated songs like Holiday by Green Day. 2 years later, our never-really-successful band broke up, because we weren’t exactly getting along and the guitarist and singer always fought so I just left. But I still play to this day (I am now 13) and I’ve learned many useful techniques. I can play a wide range of genre’s from funk to electro. So basically what you need is a somewhat powerful musical backround (musical notation, solfege, etc.), some form of motivation, mine was to impress my friend, and you have to start with the easy stuff if you want to get good.