Measure around the fullest part of the bust wearing whatever undergarment you will wear with your dress. Tape measure should be snug. 

Measure around the fullest part of the backside. Tape measure should be snug. 

Measure arm length starting at the shoulder/sleeve seam line to the wrist bone. (not the point) Then measure again from the side of the neck to the wrist bone. Finally, measure circumference at the upper arm/bicep, forearm and wrist. 

Measure around the smallest part of the waist wearing tights. This is not where your skirt hits on your hips. 

Measure from your shoulder, across the body, between the legs and back to the same shoulder. 

Measure from your center shoulder straight down to wear the skirt will sit on the hips or at the waist. Measure from that point to the desired skirt length front and back.