I was looking over my archives the other day, just sort of skimming through notes and revisions and scribbles and if I were to give my past self a few pieces of advice, they would be:
1) Just keep writing, 2) don't throw anything away and 3) put the date on everything.
They both seem rather simple and sort of "duh", but really, I wouldn't have known back then just how much I wish I'd done those things then.
1) Just keep writing. Even if an idea isn't working or you don't know how it should turn out, just keep writing it. It's sort of the golden rule of NaNoWriMo especially, but it can be applied to just about any other piece of writing. If nothing else, you'll figure out what doesn't work. In the best cases, you can end up with character motivations you didn't see coming or a plot twist that incorporates a throw-away mention you made earlier. In the worst cases, you simply have to throw out some stuff that wasn't working anyway when you edit.
However you won't really throw them away because
2) You shouldn't throw anything away. Even if that one chapter is just awful, the idea makes no sense or it's a conversation from the more bland regions of Blahsville, keep it anyway. If nothing else, you can look back on it and laugh at yourself. In the best cases, you might reincorporate it somewhere in another story or it provides the perfect inspiration for something else. In the worst cases, you at least have material for your future biographers and literary scholars to look back on and write books about.
And to help them out, you should
3) Really, put the date on EVERYTHING. All-caps was warranted there, because you have no idea how many times I've looked back at stuff I know I wrote more than a few years ago and have wondered exactly when I started writing it. Or I find a scribbled sentence or idea and I have no idea when I came up with it. If nothing else, you'll have a timeline of papers. In the best cases, you can track how long you've been on a project and keep track of your consistency and inspiration timeline. In the worst cases... Well, there really are no worst cases here. You just had to take the split second it took to write the date up in the corner. And I really do mean everything. Even if it's just a post-it note you happened to scrawl "two months instead of three?" as a note to yourself for your novel, date it. It makes things so much easier in the future, in ways you wouldn't even imagine now.
Well, unfortunately, I can't tell my past self this, but maybe my future self can put it all to good use.