Writing user scripts requires knowledge of JavaScript. The tutorials on the GreaseSpot Wiki should give you a running start on JavaScript both in general and as it relates to user scripts. Inspecting others' scripts can be helpful. You may be interested in Sleazy Forks regler for innsendte skript and Metadata om skript som brukes av Sleazy Fork. If you want help developing your script, feel free to spør på forumet.
To post on Sleazy Fork, you will need to create an account. From your brukerside, follow the link to send inn et nytt skript.