Once you've learned your basic rock beat, which entails eighth notes on the high hat (one and two and three and four and), beats one and three on the bass drum (one, two, three, four), and beats two and four on the snare drum (one, two, three, four), now what you want to think of doing is varying your bass drum for different bass drum patterns or ideas. One of the more important things is to listen to what your bass player is playing so you can vary with him as he changes his parts. You want to be really tight and execute those changes well with him.
There are countless ideas and changes you could make with your bass drum, but a good place to start is to sort of center your notes around what you've played before. For instance if your bass drum was on one and three before, maybe you add some notes around that. Let's try a variation where you put a note on the and of two right before the three, so it'd sound like one, two, and three, four. One, two, and three, four. The groove would sound like this. One, two, three, four. [drums]
If you continue with some of your eighth note variations what you could do is put your bass drum on some of the ands of the measure. When I say ands we're talking about the upbeats, the notes that fall between the counts, like one and two and three and four and. In this variation I'll put a bass drum note on one and then the and of two and the and of three. And that would sound like one, two, and three, and four. One, two, and three, and four. The groove would sound like this. One, two, three, four. [drums]
If you really want to get adventurous you could start moving towards variations of sixteenth notes, or what we all partials of sixteenth notes, and those are the notes that fall between the eighth notes on e's and uhs. This variation I'm going to put a note on the uh of two and three. So it sounds like this. One, two, a-three, four. One, two, a-three, four. Here's what this groove sounds like. One, two, three, four. [drums]
Finally, you can change your bass drum to fall on some of the sixteenth variations like e's, like one e and uh, two e and uh. In this case I'll put and e of three into the measure. So it'd sound like one, two, three-e, four. One, two, three-e, four. Here's how this groove sounds. One, two, three, four. [drums] So remember there are countless variations with your bass drum, and it's good to start in those places just to get some ideas. Remember, listen to your bass player and try to match him exactly to help the grove.