Geometry fail

scraps, originally uploaded by Hazelnutgirl.

I'm almost half way through making up blocks for my Math Facts quilt; but I'd be further along if I hadn't had a massive fabric cutting fail yesterday! The bundle in front of the photo are all strips and blocks that I'd cut, which I couldn't use because I'd cut way too many of them and then wasn't able to cut some larger pieces required for the X blocks. I am now down 3 X blocks in the scheme of things. I am really ticked off at myself for two reasons - firstly it's a big fat waste of fabric and secondly, I feel like a doofus. I'm all about efficiency and getting things out of the least amount of fabric possible and this is a blow to my self-esteem! I'll probably use up the scraps in something or other eventually but honestly! Doofus.

Do any of you know if there is some sort of rule of thumb when it comes to cutting fabric when the pattern doesn't give you a cutting order, just the total of all the pieces? Should I have cut the bigger ones first? How do you judge how many blocks you're going to get without sitting down and basically drawing it all out before you start? I want to balance caution with economy of scale.