Are you planning on going the route your Ruus showed you?
Once you get the snaps fixed to your plates, some tips are to start with the collar. Be sure to place one snap right in the very middle of your collar plate (I.e. Somewhere above your diamond). Dab some paint on your finger and put it on the rim of that "male" snap. Get your plate up as high as you can so that it sits against the base of your neck but doesn't choke you. Try to make sure it's centered as best as possible and press that snap against your vest.
If you did it right, you'll have a nice ring to center your "female" snap onto. Go ahead and set that snap and refit it, choose another snap and repeat the process.
Once your collar is set and looking good, move on to one of the other chest plates. You can temporarily tape the opposite one in place while you work to repeat the process for your chest plate.
It can work best with two people so that you can relax your arms and let the plates be fitted with your body in a relaxed position. Just go slow and take your time!