Watch the Alternating Bass Patterns online guitar lesson by Stephen Mougin from Bluegrass Rhythm Evolution
The biggest challenge is figuring out how to switch between chords and their respective patterns. Start with two related chords (say G and D) and play a measure or two of each, switching back and forth.
Once you've mastered several pairings, add another related chord (G, C, and D - 1, 4, and 5) so you can play typical bluegrass songs. Change up the order to get used to coming from the 1 to 4, 4 to 5, 5 to 4, 1 to 5, and 5 to 1. Make sure you're practicing nice and slow with your metronome.