what people have said here about having your hands out in front is VERY true. its especially true for moguls....because so much is happening at the one time you can forget to keep forward pressure. hands out in front helps.
if you want to know how much pressure you want on the tongues of the boots imagine you have a coin there. you want enough pressure to keep it at the top of the tongue but not so much pressure that it bruises your shin.
there is another thing though...a few years ago i was really confused because i put pressure forwards like my instructor told me to but my tips were overly sensitive. after a while we realised that it was my first pair of centre mounted skis so i didn't need to lean forward a much to initiate the turns. i could afford to be more centred. if, however, you go to full on racing skis like my skiercross rossis then you need a LOT of pressure forward on the boot to turn them...so its just a matter of working out how much you need before the tips become overly sensitive.