[ HELP!! ] Proper way to measure Armour for Cosplay.

Hello all, I dont know if this has been asked before. I am very new to 3d printing and to this forum. I was wondering if anyone had good information on a proper way to measure your body for Cosplay.. Ive seen a few videos from prop makers for cosplay. But they never show really how to measure properly at all. Example: Shoulder Width/Length etc etc.. I have been trying to size this pieces of mine but they have turned out either to big or small. I am using calipers as well. I am just lost on to really measure. :P Thank you in advance for your guys help. Cheers!