Accurate measurements are very important for a good fit! The measuring tape should be parallel to the ground for all measurements, and snug but not pulling tight. You may need someone to help you.
Basic Measurements:
High bust - wrap the tape under your armpits and above your bust, and relax your arms down.
Bust - wrap the tape around the fullest point of your bust and relax your arms down
Waist - measure around the narrowest point of your waist, or the hinge point when you bend sideways, and RELAX (don't suck it in!)
Full hip - measure at the widest point (this will be higher or lower depending on your shape)
Other measurements:
Torso length - tie an elastic around your waist, and then measure from the base of your neck (at the bone) to your waist
High Hip - measure at your hip bone
Sleeve length - measure from your armpit to desired sleeve length (or measure the underarm seam of a similar shirt)
Inseam length - measure from crotch to desired hem length (or measure the inseam of a similar pair of pants/shorts)
Shoulder width - measure between the outside points of your shoulder blades OR measure between the shoulder seams of a non-stretchy shirt that fits really well
Skirt length - length from waist to hem
Shirt length - measured from the back collar to hem