1. when you hold your cutter, you want your hand and wrist to be at a nice straight line (you can either have your finger extended above the upper surface of the cutter or not - it's whatever works best for you). all your joints should be limp and your muscles should be relaxed, not contracted.
you want an elongated arm with a cutter at the end that needs to feel like a natural extension of your arm.
2. do some test runs over your cutting mat (without the fabric) to find your most comfortable position. your cutter needs to glide easily without much pressure from your body.