The basic exercise for this is playing straight 16th note.
The beats shift from finger to finger, since you play groups of four with three fingers.
Assuming you play the "Billy Sheehan" way, meaning ring(r), middle(m), index(i), and repeat - it goes like this:
Code:
1 2 3 4 | 2 2 3 4 | 3 2 3 4 | 4 2 3 4 | etc.
<b>R</b> m i r <b>M</b> i r m <b>I</b> r m i <b>R</b> m i r etc.
So the accent shifts from ring finger (1st group) to middle (2nd group) to index (3rd group). After three groups of 16th it repeats.
If you're not careful, you play the accents on the same finger, turning the whole thing into triplets.
Exaggerate the accents at first, practice slowly, and you'll soon get the hang of this.