Day one: Write out a one-page summary of your story idea. Then write half-page bios on all your main characters so you can get a feel for them and who they are, how they speak and what they want in life. Then break your story into beats or scenes to create a full outline. Most scripts have around 40 beats or scenes.
Day two: Obtain a copy of screenwriting software. This will save you tons of time as it does automatic formatting so you don't have to worry about getting every line straight and properly positioned. There are lots of different programs out there, but the industry standard one is Final Draft. Install the software and spend the day getting used to all the functions and keys. Most have tutorials and examples you can study to learn more.
Days three, four, five, six, seven and eight: Print out your outline and have it by the side of your computer at all times. Write your screenplay. Keep writing even when you get writer's block. You know what happens next in the story--that's what the outline is for. It may not be perfect but keep writing and chugging along. You should aim to write 20 or more pages a day. If you do get really stuck or just need a break, go out and take an hour off. Go for a walk, play with your kids (if you have any) or do some chores. At the end of day eight when you've finished the script, print it out and give a copy to a few good friends or family members. Ask them to read it and write out their critiques.
Day nine: Rest. Set the script aside and don't even look at it. Take the day off to clear your mind and free yourself entirely from writing. If your friends and family members give you the critiques back, great, set them aside until tomorrow.
Day ten: Get up early, refreshed and ready to work. Sit down and reread your script front to back. It probably looks very different now that you're not focused on it every minute. Take notes on things you see wrong such as typos, and also note things that you don't think work well for one reason or another. Then read the critiques from your friends and family. Consider all their points and decide what you will take away from them. Then sit down at your computer and start rewriting. Go back through each page and fix those typos, alter the dialogue and/or completely rewrite some scenes. When you're finished you'll have a complete screenplay, ready for Hollywood to read.