First thing you want to do is measure shoulder to shoulder at the widest part, usually where the sleeves end on a t-shirt. Add 1.5″ to either side to account for seams
Next measure the length of the back from the lower neck to the midway down the thigh. Adding 1.5″ to each side to account for the seams.
Measure from your collarbone (neckline of a t-shirt) to midway down the thigh about 2″ above where the back pattern was measured. Add 1.5 inches to each side to account for seams
Measure around widest point of chest/bust. Add just 1.5″ to account for seams
Measure from the top of the shoulder to the end of your wrist. Add 1.5″ on either side to account for seams.