You have a couple of choices; 1) wing it or 2) play sheet music by rote. Either way sheet music by rote should be in your future. Lets address winging it.
You fingers need to know what to do - so scales and patterns.
www.studybass.com
Your ear needs to know the good notes from the bad ones - so scales and patterns.
What would I have you do - scales and patterns. OK which scales? The Major and natural minor scales. Which patterns? The Major and natural minor scale paterns. Yep kill two birds with one stone.
When you get bored try studying how to compose bass lines and then use them when jamming to the backing tracks and the music videos that are on the Internet. Gotta get to where you can
hear the chord changes.
Goal is to play songs. Have one new song on your list each week. NO not from tabs, tabs will just slow you down - bass clef, lead sheets or fake chord.
Here is a start.
http://www.ultimate-guitar.com/tabs/...e_lamb_crd.htm
Or let Google find you some fake chord -- Google these key words; chord, "name of the song" -- the comma and quote marks help.
Here is a goal.
http://www.youtube.com/watch?v=R4x0u...eature=related