Measure with your arms outwards measure around the fullest part of your bust.
Measure around the waist, if you are unsure of the location slightly bend to locate it and then measure standing upright.
Measure around the fullest part of your hips. (Not just hip bone to hip bone).
Measure from thorax to floor ideally wearing your desired heel height.
Note: It is always more accurate to have someone else measure you where possible. Do not pull the tape measure tightly.