If you lift something, lift the ball-of-foot, not the toes. Your instructor will never know; he can't see inside your boot. Bend forward at the ankle, INTENTIONALLY, with muscle action, to get the ankles to dorsiflex. Here's the muscle that does that:
It does not lift the toes. So toe-lifting doesn't tend to work to bend the ankle forward. You need that lower leg to tilt forward. Toes won't do it. Your instructor will be so happy to see your belly button forward and your new ablilty to lift the tail of the ski that he will assume you are on the ball-of-foot.
This ball-of-foot thing won't be useful until you're on snow. And if you're not certain, just train yourself to be able to stand on ball-of-foot, then on whole foot, then on the heel with the ball-of-foot lifted, all the while bending forward at the ankle so you have shin-tongue pressure and while moving your belly-button forward. If you can switch at random on purpose, then you can check out both on the snow and see which works best for you. Versatility is always a good thing. On the carpet you have the perfect opportunity to work on these subtle but difficult to learn things. You don't run out of space and have to get on the lift, you don't have 5 year olds crossing in front of you, you don't have inconsistent snow and inconsistent pitch. It's a great learning opportunity.
If you fail to keep the ankle bent forward, and if you fail to move the belly button forward, then lifting the ball-of-foot will be VERY BAD for your skiing. It will put you in the back seat fast. This may be one of the reasons instructors don't teach their students to balance on the whole foot. To stay out of the back seat when the heel of the foot is weighted, one must also move the weighty upper body forward.
Here's an exercise for dorsiflexion. It will help you feel your tibialis anterior muscle working:
Here's one closer to what we do when skiing:
Does this make sense?