Determine whether your script is actually ready and finalized for printing and binding. Have someone proofread it at least three times, format it correctly and make sure it won't need any other major revisions.
Print the number of copies you need plus three. If the total is greater than 20, you may want to increase the number of extras you have on hand. Take into account that people lose their scripts or ruin them in various ways. It will be a bigger inconvenience to have it reprinted later, so do it now.
Collate the scripts so that they're in order and ready for hole-punching. It's a major task to sort out 25 copies of a 100-page document. To avoid headaches, check your page collation or use a service that can do the copying and collating for you.
Punch three holes along the left side of your scripts, separately. Make sure you keep the script pages clean and unbent.
Decide whether you'll be using a cover and back page. A thicker stock paper is a great way to give your script some support and help it survive wear and tear. If you decide to use one, put the cover, also three-hole punched, on top of each script and the back page on the bottom of the pile.
Put one brass-plated fastener in each hole and secure it by spreading the prongs outward on the back of the script. Make sure to use the right size of fastener. The right size leaves about a half inch of metal on the back side, enough to fasten securely.