When starting your rough draft, know it's okay for it to be just that: rough. Be sure to start the writing process early to leave yourself enough time to create several drafts.
If you find yourself becoming frustrated or hitting dreaded writer's block, walk away from your words. Take a break! A few hours away from your draft can clear your head and allow you to bring a fresh attitude to the next time you decide to tackle the writing.
Remember: if there's one thing to know about drafting, it's that multiple drafts are your greatest tool. Each draft allows you more time to think and revise, creating a clearer and more effective piece of writing. Now go--draft on!