The most basic way to approach rock bass lines is by "pumping" eighth notes as a steady stream. This provides a very solid background and, although it's "busy", in the sense that every possible subdivision is played, it doesn't SOUND busy. It just stays there in the background, doing two of three possible jobs: rhythm and harmony (in this case laying down the ROOT).

Few bands survive by playing lines this elementary on every song. Let's look at some ways of generating more excitement.