I also agree with Carmine. Just listen to the song and get the "feel" of it. I usually start tapping my feet or hands along with the rhythm. Another thing I've found that helps is learn the lyrics to at least one verse and sing along. Then when I feel I'm close, I pick up my guitar, mute all the strings with my left hand and focus on just strumming the rhythm with my right hand. Final step is adding the chord changes. Knowing the feel of the song usually makes this part a little easier.

Denny