Bust
At the fullest point of your bust, measure your chest using a measuring tape that is slightly relaxed. For the best results, do not wear a padded bra while you do this.
Waist
Do a slight bend to find the natural indentation of your waist. Wrap the measuring tape around your waist starting and ending at this point. Keep a finger between your waist and the tape - this will give you a comfortable, accurate fit.
Hips
Keep the measuring tape parallel to the ground. Wrap it around the fullest point of the hips and buttocks. It will be approximately 7-9 inches below the waist.