Watch the SECTION 5: The Bass online guitar lesson by Susan Mazer from Hands On Guitar: Beyond Beginner
Go back to some of your existing tunes and try creating a few bass lines of your own. Add slash-chords to a basic chord progression and you’ll hear how they add another level of interest for the listener. Also, start listening more closely to the bass lines in songs. They are the unappreciated glue that holds the tune together.