The important thing in your first draft is just to keep writing. Even if you realise you've just used a stereotypical description - 'red as a beet', etc – unless you can come up with a better one immediately, just leave it there for now. If you're truly worried that you won't notice how bad it is, use an asterisk or footnote e.g. 'red as something unusual that fits into the store: ruby? traffic light? fresh blood?'
Then move on. No matter how beautiful a sentence seems as you write it in that first draft - it's highly unlikely that it'll remain in that form in the finished book. So relax, write, and when your story is done and needs tidying and editing, be absolutely rigorous about these five tips.
Good luck to everyone doing not just NaNoWriMo, but taking that brave step of leaping into any new writing!
