The ideal foot has the "widest" part of the point just below the ankle. Although not everyone has the naturally beautiful foot, there are some things everyone can do to have a perfectly acceptable point.
First: GET YOUR LEGS STRAIGHT! When the leg is straight, all of the foot's arch can be seen. One thing that often keeps the legs from straightening is not having the back straight. Be sure to keep the hips tucked so the back will be straight, then the legs can also be straight.
Second: Stretch your pointe. Being extremely careful to not allow the foot to scicle either to the left or to the right, apply pressure on the top of the foot where the arch ends. Hold the pressure for at least 3 minutes to trigger muscle memory.
Some dancers have a nice pointe, but don't always point their toes. Be sure to not just point the foot, but the toes as well. Also called articulating the toes, getting the toes down will improve the appearance of the foot's arch.