bust: measure around your chest at the fullest point of your bra cup. make sure to go under your arms, not over them
waist: measure around the smallest part of your waistline with one finger between your body and the measuring tape.
dress length: stand with your heels together, keeping the tape straight and perpendicular to the floor. measure from the high point of your shoulders down the length of your back.
inseam: find a pair of pants that fit you well and measure from the crotch seam to the opening at the bottom of the pant leg. round to the nearest 1/2" to get your inseam length.