I went over this in another thread so you might want to do a search.

Basically most Celtic music is done in a myxolydian mode. It's only sounds technical, you only have to learn one shape and five notes.

You need a drone effect so here goes. The key of D is a common Celtic key. The lower A is the drone. So here's your pattern, D on the A string, right beside is the A on the E string. You'll go one note (two frets) on the E string (A to B). You'll go two notes on the A string (two plus two frets) which is E to F#.

Amazing Grace: A-B-D, F#-E-D-F#, E-D, B-A

There's your shape, it repeats on the D string 7th fret and the B string 10th fret. Use the A string as a guide, key of C, third fret, same pattern.

Play around with it. Always finish on the D but try to keep the A note fairly constant.

Then you have to learn to play broken triplets. It's not a four count and it's not the blues triplets. Think Riverdance.