When I initially begin a first draft, I generally have only a hazy idea of where the book is going to go. I almost alway have a hook, a beginning, a smattering of characters, and an ending. It's all that middle stuff I lack.
The final draft usually looks nothing like what I thought it would look like. AND THAT'S OKAY.
First drafts, in my opinion, are for experimenting. Messing around. Peeking in all the dark corners to see what's there. I was running the other day, and I, for some odd reason, recalled the question: If a tree falls in the woods and no one is around to hear it, does it make a sound? Everyone's heard that, right? But the scorching heat boiled my brain and I started thinking about why writers need solitude for a first draft. It's because we're trees in a forest. If no one's around to hear us fuck up, then it doesn't count. Right?
You should feel comfortable trying ANYTHING in a first draft. If it doesn't work (and it probably won't), you can always take it out before anyone reads it.
During the first draft of FML, I was struggling with structure. The hitch in FML is that it's two stories side-by-side, that have to be unique but similar. I've got to cover some similar ground while keeping both fresh. I'd decided to try to write it in third person...with each character taking over narration at different points throughout...AND I tried this thing where each of the narrating characters broke the fourth wall and spoke directly to the reader. It was a failed experiment. Badly failed. But it helped me with my characterization. It helped me pull the characters apart and figure out who they were, what their motivations were...what they wanted. And in the end, those botched attempts at a first draft were responsible for the final draft you'll get to read next summer.
That's the beauty of being a writer...no one has to see anything you don't want them to see. So feel free to write all the things you're scared to write. The jokes you think are too dirty, the emotional scenes you think are too raw. Write them all. They might end up on the cutting room floor, or they might end up taking you places you never imagined.