Bust: Measure at the largest part of your bust leaving the measuring tape loose and comfortable.
Waist: Measure at the smallest part of your waist while still remaining comfortable.
Hips: Measure around above your thighs and below your waist. The measuring tape should be around your hip bones.
Inseam: Measure from your inner thigh to the floor. Don't forget to account for the type of shoe you will be wearing. If you don't have someone to measure you, another trick is to measure a pair of your jeans from between the legs down.