Stand in front of a full-length mirror. Remove all your clothing, except for your undergarments. Try to wear the same undergarments you will wear on the day of the wedding. A well-worn bra may be comfortable, but if it sags, so will your dress. If you intend to wear panties that hold in your tummy, measure yourself while wearing the same type of panties.
Stand in a natural position with your weight distributed evenly throughout your entire body. Do not suck in your midsection. Make sure your feet are flat on the floor.
Measure your bustline by taking a cloth measuring tape and wrapping it around your back. Bring the ends together over the fullest part of your bosom. Make sure you do not push in your bosom. Write down the inches for your bustline.
Tie a piece of string snugly but not tightly around your waist and bend your body from side to side a few times. The string will fall naturally to your waistline. Take your tape measure and carefully wind it around the string. The point where the tape meets is the measurement of your waist. Write that on your paper.
Wrap the measuring tape around the fullest part of your hips, making sure that the tape is parallel to the floor and there are no dips in the tape.
Measure from the nape of your neck to your natural waist and then from your waist to where the dress will hit your legs -- knee, calf or ankles. If the dress will be full, measure at an angle to allow for the extra fabric.