Pea - By the Red Hot Chili Peppers (This was the first song I learned)
Smooth Criminal - By Alien Ant Farm (The seccond song I learned)
Smells Like Teen Spirit - By Nirvana (Amazingly simple yet fun to play)
Soul To Squeeze - By the Red Hot Chili Peppers (This was a HUGE step for me)
Next I focused on scales and theory for a month or so and Finally i spend another month learning all the Red Hot Chili Peppers songs, well the simple ones atleast. Now im working on slap bass and "Pretty Little Ditty" (you know, that song Crazy Town STOLE their main riff from which made them popular?) and next im hope to learn most of the System of a down songs and then work on some more theory, mostly so i can start creating bass lines.. (scarry thought)
All in all what has helped me the most is listening and playing the songs at the same time over and over (and over and over...). Having the song playing at the same time you play helps you keep the beat and sounds cool cuz you have some drums and a guitar in there too.
This is just how i started, I hope it helps, also I constantly play with guitarists. Guitar and bass together sounds amazing.