Well, I actually have a very weird way of making MoCs.
1. I draw up a concept piece for the character I have in my head.
2. After that's all done, I grab a random piece and work my way around it, finding ways to create a good custom torso, since I always start out with that part of the body.
3. Repeat for the limbs, and the head if necessary.
4. See that my MoC looks like trash and revamp it over and over and over and over...
5. Actually become satisfied with the final product, then most likely end up destroying it for parts. Unless its my self-MoC, then it's safe.