Drive up onto your toes by pushing your big toe into the ground HARD. This will help you get all the way up into a true calf contraction, unlike the half-repping stuff you’ll see other people doing.
On the way down, allow your heels go slightly lower than the machine. This will create a slight stretch at the bottom of the rep, but there’s also another useful benefit to doing this; the seated position will enable you to hit the tibialis anterior (the very thin muscle which runs up the shins).
