Long post incoming, but this is how I go about scripting some simple tricks. I'm coming up with this as I type it.
The way I like to come up with a script is first starting off with where and who I want to perform for. I find myself always meeting new people through friends of friends and occasionally someone will say, "Did you know he does magic? Can you show John Snow something?"
Okay so now I know who I want to perform for: A stranger. Male. Around my age (26). In front of a small crowd. At somebody's house or at a restaurant.
Next is: what do I want to say? Do I want to perform something that will introduce myself? Give him my business card? Give him my phone number (lol)? What do I want to accomplish by showing this guy a magic trick? Something my girlfriend always talks about is how men have fragile masculinity. A lot of men are afraid to look gay, or girly in anyway. So I kind of want to play with that idea. I want him to feel some what uncomfortable while playing with this idea of fragile masculinity, but not so uncomfortable that he is turned off by me. So it has to be funny. To him and everyone around. And it can't step on anybody's toes.
Next is the trick. What do I actually know how to do? Should I create something original, or use a trick that already exists? I think if you're new to magic, and practicing scripting, you should use a trick that already exists and create the patter around that. So for this impromptu example I'll use a trick taught by Chris Ramsay here:
Now we need to break down the trick. What is it at it's core? It's a pick a card, find a card with my signature jumping onto a card with his signature. This is where creativity comes along.
Instead of having him sign the card with his name, I tell him, "I want to try something a little unconventional. Don't sign your name this time. I want you to actually write booty hole on there. If you will. Please
". As I pull the card back, I blow on the ink and ask, "Do you like it when I blow on your booty hole? I'm just rubbing it to make sure your booty hole is dry. Okay look, I'll place your booty hole in the center of the deck where it's warm, comfortable and safe from any more harassment. For now."
I'll spare you the rest of the scripting, but basically my signature is a drawing of my p****s, I get him to hold my p****s (the drawing), throw it back into the deck, and find it on the card with his booty hole on it.
I came up with all of this just now. So what's next? Practice it! Sometimes things sound good in your head, but are terrible when applied in real life. Say it out loud. Record yourself. Listen to your recording with your eyes closed. Watch your recording with no volume. Watch the whole video in full. Keep a note pad next to you. Then test drive it!
Good luck. Get creative. Hopefully I've provided you with a sort of template to help you get started on working on your script.
Sorry for the long post.