I didn't see it mentioned (maybe I missed it)-
Anytime I make anykind of notable change, I do a "save as...". I put a double digit number after the project name (and maybe sometimes a description of the change i.e. "bass OD" etc). So start with "Project Name" and start saving "Project Name01", "Project Name02", or something like that. It's basically a manual form of what autosave does, so If there is a crash or i decide my project has taken a turn for the worse, I have something to go back to.
Tip: use double digit numbers! (01, 02, through to 99 which you probably won't exeed). If you write "Project Name 1", when you're browsing through your folders things won't be laid out sequentially. It's a simple thing and I could explain it better if I wasn't sitting in on a pretty wacky project right now