Two things that helped me understand drummers is 1) talking to drummers that I know. Asking them how they come up with beats to guitar riffs, and just cool little tricks and fills they do. I think thats your best bet but if you don't know any drummers. You can try looking up drum tabs on the internet to see what certain drummers do. That's how I picked up alot of ideas and got the feel for how it works. Drums are pretty straight forward, all you need to do is tap out a simple beat to the music your playing. You might just be trying to make the drum parts too complex. Most enteraining drum parts are rather simple then liven up on a fill.