Writing Tips for that First Draft
Write, write, and write some more.
Read, read, and read some more.
Whether or not you write an outline for your work, when it comes time to write, don't stop. Follow the outline, but don't go back to edit. If you absolutely must, write a comment to yourself in-line or use the comment feature if your writing program has one. When I write in-line, I write in all caps and highlight the text so I can't miss it the next time around.
Don't check grammar or spelling. Either your writing program will let you know what's wrong, or you'll pick it up on the next draft.
Try joining a writing community like NaNoWriMo. Every November, NaNoWriMo hosts a challenge to write 50,000 words in one month. It sounds impossible, but following their metrics, it's totally possible. The first time I participated, I hit 100,000 words, and in subsequent challenges, I made my goal of 80,000 words each time. The secret is simple: If you write 1,667 words per day, you can absolutely hit 50,000 words in a single month. The website has multiple features that help including word counters, forums, and connections to your local in-person groups. It's a pretty nifty system.
Finally, enjoy yourself. Your draft might be a mess, as mine always are, but it's the beginning of a great story. You can revise as many times as you want, but you can't edit a blank page.