Reddit mentions of Steve Kaufman's Four-Hour Bluegrass Workout

Start with some fiddle tunes! I'm a big fan of the Kaufman 4-Hour bluegrass workout books for learning some. They have a bunch of tunes, most of which are jam standards, in music and tab, and include CDs with slow and fast accompaniment so you can practice with a band. Once you have the basic tune down pat, work the same thing up the neck, and then do some improvisation around the melody.

For rhythm playing, be sure to find resources that teach you proper right hand patterns. Bluegrass guitar is all about the "boom-chick", where you play a low string on 1&3, along with the bass, and strum the chord on 2&4, along with the mandolin, everything on downstrokes. You can go beyond that of course, playing on upstrokes and syncopating, but I see a lot of young and beginning bluegrass guitar players strumming like they're playing a folk song, and it just doesn't sound good. Also learn some bluegrass runs (start with the Flatt lick).

Finally, do some listening. Tony Rice's work on the Bluegrass Album Band records is the benchmark for bluegrass guitar IMO and a good place to start. Listen to how he keeps it simple most of the time, and how tasteful and musical the accents are when he changes it up with a lick or extra strums.

I have a few suggestions. The first is a series by Dan Miller and Tim May that they sell that progressively builds on older material and builds chronologically. That link I included should link to pages where you can view more closely the material in each book. I trust you to know your own skill level and what you want to learn to be able to determine what book you want.

Another one that I've heard is pretty good is the Real Bluegrass Book by Matt Flinner. It has musical notation and chord backup for a bunch of standard bluegrass tunes.

Not knowing your skill level, I'll throw in this last one because it was a good one helping me to get started with: the Four Hour Bluegrass Workout from Steve Kaufman. While I'm not the biggest fan of Kaufman's flatpicking, the guy's written some really great teaching tools for flatpicking fiddle tunes. And flatpicking fiddle tunes is a great exercise for practicing bluegrass.

Edit: If you have any luck with any of these, or any other book, please let me know!