When you are not sure of a part, and it is your first draft, keep writing. Just skip that part.
When you are writing your book, story, screen play, poem, whatever…. and you get stuck. Call it writer’s block, call it a block of any kind, plug ahead. Just ignore that part that you are having difficulty with and skip ahead to a part that you can write.
Don’t just sit and wait for inspiration to take over, or for your character to scream what she/he needs. Leave a spot open on that page where you can go back later when you have your ideas in place, and move ahead to the stuff you already know.
Don’t stop writing. Just keep going.