Adding on to Snowolf's response... On heelside's, bend your knees and drive your hips towards the snow, while maintaining an upright body. Get the board high on edge. Higher edge angles have better edge hold. Try some drills where you change the angle of the board (mid-carve) solely by driving your hips uo and down, then solely by bending your ankles up and down. That works great to help you feel the relationship of each. Also, try setting your highbacks forward so your calves have something to brace against. Your heelsides should become much more powerful.