Bust
Measure over the fullest part of your bust, in your best-fitting bra

Waist
Measure at your natural waistline, at the narrowest point.

Hips
Stand with your legs together and measure over the widest portion of your hips: this typically include the fullest part of your rear

Inseam
Lay your favourite leggings on a flat surface and measure from the crotch downwards, following the inner seam.