That's a big question. Get the book Comedy Writing Secrets. It had a huge impact in my writing and my sense of humor.

Once upon a time..

If this works I will give you no credit....once upon a time it is

What type of comedy are you thinking about? Satire? Slapstick? Do you have a vague outline of the script in your head, or are you just going with the flow?

Really big question. Sorry to answer a question with a question, but for the best answer please post the following:
- what kind of script is this? Ie: a speech, a short film, a vignet, play, stage show, stand up, tv show, movie, etc?
- what Is it? Are there characters and a plot, a one person show, is it meant to carry a message or entertain, will it need blocking and other details (where people stand at different points, their reactions and action, camera angles, sounds, music cues, cuts, etc?)
- what have you done already? Do you have an outline? Have you done any research (if needed), do you have any drafts, any materials like character info, set pieces, scenes, lines or jokes to include?
Style wise you can go in to a script with as little or as much work already done as you want- either way you’ll likely do some reworking during the scripting. It’s good to have an overall picture before you start. A script is just an organizational tool though.

Smoke weed.