Tremolo is a great technique that has been seriously under-deployed in the world of bluegrass guitar. Michael Daves from NYC is maybe the only flatpicker I've ever heard who tremolos, and when he does it it's righteous. The secret to playing good tremolo is subdividing the beat into smaller beats, in this case I'm subdividing them into 8th note triplets. You should practice playing the subdivision first - tapping your foot should help. Once you've got the hang of it and you start to feel the big quarter note in your hand (this will be every 6th note), then you can start trying to play melodies with the technique.
Have fun and be creative with it - playing the tremolo in bluegrass guitar is kind of like the wild west, so get in there, figure some stuff out and show the rest of us what you're up to!
ChrisTopics and/or subjects covered in this lesson:
With Body and Soul
Loop 0:00 Run-Through of Melody to With Body and Soul with Tremolo
Loop 0:46 Introduction to Tremolo
Loop 2:55 Breakdown of Tremolo Technique in Bluegrass Guitar
Loop 9:27 Closing Thoughts and Outro