Patience is key.
Also, when you go to scale a piece, if you are going to slide it on and not split it, measure the narrowest part of the piece and the widest body part it will need to fit over (e.g. the neck on a helmet and your head). Take into account any padding/foam you're going to put on the inside for your measurements. And if you can figure out from the file which pieces make up that smallest part, try to make that first. It will save you lots of time building only to have an armor piece you can't use and have to re-scale.
Make sure you read the warning labels when you get to the resin, fiberglass, and bondo stages. Both resin and bondo are toxic, so it's highly recommended you wear a respirator and work in a well ventilated area. When sanding, I highly suggest wearing either the respirator or at least a mask to keep from breathing in the dust.
Start with something that's not very detailed (don't start with the helmet). You need to get accustomed to the techniques and detailed pieces are not great for learning. I've learned that one that hard way and will be backing up to something "simpler" on my next piece.
Other than that have fun with it. You're making Halo armour after all!
