I've been taking mine really slow, and working from the legs up. The legs are the easiest shapes and you can also use them to scale the other parts. My advice is - don't try to tackle the torso first if you haven't played around with materials that much - you can figure out how things bend and conform to your body doing arms/legs. But DudeShep doesn't have boobs, so he has that part much easier
But I wont lie, its very hard work.
@soren - I may be heading up to NYCC next year with this costume, just FYI. And I've given some thought to selling some of the the unpainted, vac-formed parts of this suit when I am finished. As of right now I need more practice with vac-forming though.