Ok I feel a need to step in...
The heel-toe technique is NOT a heel an toe there is actually NO HEEL STROKE!
The ''heel stroke'' is actually a toe down stroke.
For example, if you want to start with toe up stroke or toe stroke, rise ur upper leg and in the same time move your foot down. This part is pretty simple, now comes the hardest part, now the toe down stroke or the ''heel stroke'', it is the opposite, you have to move your upper leg down and your foot up (just a bit) so now you have the double stroke motion. Now try to keep it fluent.
If you don't understand my explanation watch the
Jojo Mayer's Nreve video clip from MD 2005
(1:33 min) as you can see, his heel never touches the foot board (well it does, but not in order to make a stroke)
also, check out Steve Smith's DVD - The History Of US Beat, great explanation of the heel-toe technique.