I think the Arbans are wonderful as far as a double tonguing regime. Take an exercise a week.. use your metronome and practice one a week. The other thing to do is find the characteric studies that have double tonguing in them. Pick one a week as well.
The Clarkes are great yes, but for some reason I find the Arbans have a well laid out progression. The trick is to do them everyday with a metronome.