Take an AM/FM radio with you and try to find a station that plays old standards. You know, Frank Sinatra, Sarah Vaughn, Glen Miller, that kind of stuff. You will probably never have a need to play this type of music. You may even think that it kind of sucks. But that doesn't matter. This old time music usually had a melody to it. And best of all, it had interesting chord progressions. Some of these songs used 30 or 40 chord changes in one verse and chorus. Not like some modern music in which 3 or 4 chords are enough for a whole song. Here's what you do. Hum or sing the bass line along with the music. The first step to being able to play lines and intervals on your bass neck is to hear the notes in your head. The next step is to make these ideas come out of your bass. This "ear training" will help you to be able to take any musical idea that comes into your head and transmit it directly through your hands. When you get good enough at it you will be able to play any music that you hear, automatically. In prison we had a lot of time on our hands. They wouldn't let me have a guitar or bass in my cell because they were afraid I would hang myself with one of the strings. So I spent many hours singing bass lines along with old standard tunes on the radio. I'm a better player today because of it. Give it a try.