Practicing scale intervals on guitar in 3rds, 4th, 5ths so on is a really effective exercise. Try it in 4 ways:
1) Ascending
2) Descending
3) Ascending - Descending[1st 2 notes 1 and 3 ascending next two descending that is 4 and 2 and then 3 and 4 and then so on]
4) Descending - Ascending[Opposite of 3]