The "diddley diddley diddley" rhythm suggested by a poster above is helpful.
I would try starting off by just playing 4 notes, the first 3 being on the beat, the last 1 slipped in as an extra rapid step.
In terms of "diddley diddley diddley" the first 3 would be on each "di" , the last 1 would be on the last "ey".