Low angle shots do two things:
1. Makes the character look more menacing or powerful.
2. Makes the character look taller.
Use low angle shots when practical.
When a low angle shot is not practical:
As you stand, extend your rearward leg out and point your toe away from the camera. That will add to the illusion of length. In a straight on shot, point the toe nearest the camera toward the camera. Again it will add to the illusion of being taller.
Heels make you look taller as well since they basically force you to stand on the balls of your feet.
Many cosplayers have fooled themselves into believing that platforms make them look taller. They do not. They just make your feet look enormous. Avoid them.