try your best to keep the base material for any pre-cut formers and ribs etc to act as templates. If the pre-cut parts are loose, draw their outlines on some paper and keep it in the box. So if you make a complete mess of something, you can make another kit of bits. Or even make another complete model!
The advice about keeping things together and tidy is really good. I try to do this, and always fail somewhere, usually with an indispensible scale doodad that usually winds up in the freezer, or at the bootom of a tin of varnish.
I make notes in the user manual about TX set-up etc, sub-trims and the like, so if the TX dumps my settings, I can re-programme immediately without trial and error.