Arm - some do it down at the side completely relaxed, some do it with the arm straight out to the side, palm up - measure about midway between shoulder and elbow
Chest - even with the nipple line (try to be a mid-breath)
Waist - at belly button (or natural waist line)
Hip - 6" down from waist, or at largest point of bottom
Thigh - 7" up from knee
Calf - at largest point
I have seen of variations and different locations, but the main objective is to measure the same places each time to minimize variations in measurements.