So you finished that first draft and you're unsure what to do next. Don't worry, there's not a writer alive that hasn't run into this problem. Advice will vary on what you do next, but in the end that's up to personal preference.
For me, after I type "the end" I like to jump write back into the beginning of the book and start draft 2. I know, I know, authors X,y, and z all say they put their drafts aside to start the next project, so in a few weeks they can come back with a fresh eye. Look, I get that, and I get the reasoning behind it. It even makes sense to me, but still, that method hasn't worked for me. Not for a novel, not for a novella, and not for a short story.
You see, your good friend John Lynch has a brain like Swiss cheese. Years of substance use, various forms of physical and mental trauma, and not taking care of myself physically or mentally has made my memory more like that of a gold fish than that of a human. If I come back to a draft after a few weeks, I'm like a lost child wandering through the market, crying with a pants full of piss hoping I don't get abducted.
Starting from the beginning immediately is something I swear by. You see, when I do that, the middle and end of the book are close enough that I feel comfortable knowing where the story went that when I'm starting draft 2, I can make sure that how we got there makes sense. Without good notes, and giving myself time to forget the story means that I also don't remember if something I wrote at the beginning doesn't jive with something in the middle or the end, but if I started immediately on draft 2, I can fix those early points that no longer work with the direction I took the story. I fixed more than a few major points this way with The Warrior Retreat, and it also allowed me to know that at the beginning I had to better flesh out certain characters and friendships.
One thing that is consistent no matter author you talk to, is that your first draft is probably a piece of shit. Just write the damn thing so you can get started on draft 2.
If you want to see how that method worked for me, don't forget you can check out my Novel, The Warrior Retreat. The end result is something I'm proud of.
