Keep your heels low and still, wear the right shoes for the job
Can't think of any great training, just practise and messing around bouldering on easy slabs, Although one thing I sometimes do as a warm up is put one foot on a knee height rock and bounce onto it without flicking off your toes on the lower foot, or really digging with the high foot. Just try and float up from your knees/hip/core and try on various heights and from different angles, piroueting onto it etc. Obviously you look like a complete twat as you do this. But as slabs get thinner it's quite important to be able to move your weight onto your higher foot without stomping onto it or sharply pushing/flicking off the lower foot causing it to slip