Many bluegrass runs are based on the Pentatonic major scale.

In the key of G: G A B D E ending on G again.

The blues notes that can be added to the scale are the flat 3rd Bb and the flat 7th F natural(sometimes the flat 5th but not usually).

The famous G run is G (6), A Bb B (5), D E D (4), G (3).

After you get the hang of the G pentatonic major with blues notes, you can venture into passing notes and chromatic scales.

I've started playing more chromatic scales this year and they really gives you some nice bass runs and fills also.

-Richie