The person being measured should stand straight, on both feet, feet some 15 cms apart. It is better to wear fitted clothes when measuring. It will be perfect if you can wear lingerie you intend to wear with the final garment, while taking the measurement.
Don't make assumptions on size; always measure first. Use the factory edge on a piece of lumber whenever possible, especially when squaring up a perpendicular cut. It will make everything fit together better. Not all tape measures are created equal.
