I write short novels and novellas, mostly. I write the blurb first -- usually a longer version than the one I'll actually use as the blurb.
If it doesn't work, the storyline probably won't.
Then, once I'm satisfied, I start the first chapter, usually introducing and fleshing out the main characters. If it ticks, then I know I can get into writing about them.
Then I add other key elements a page or so below the bottom of the document -- far enough away from the body to not get in the way, but close enough for easy access. It, naturally, gets removed before preparing the document for publishing.
For longer novels, I do not know what would work. My way of doing it would probably be more or less ineffective, but it's better than nothing.