Pattern pieces. Seriously, never just wing it when you're building something. I actually used a full body-suit costume pattern to get the shape down since I had it handy (as you can see, I kinda screwed up on the length on top...have to add about a foot extra to it now).

Never start with the fur, You will just waste more material than you'd ever need to. Instead, get a machine cotton or a muslin fabric and make whatever you're crafting with that first: it's cheap, you can use it to get the perfect fit, and it'a also very handy for marking pieces for doing a design with color in the actual pattern pieces themselves (think Starlight's body...all that done with almost 0 wasted fabric)

Also, don't forget to cut out your notches! They help a lot for lining stuff up.