I don't think I'd hear any arguements or even serious discussion on the matter, by stating that the mIRC scripter's bible is the help file.
/help
There are several sites that also have tutorials, but for the beginner, even these tutorials can be confusing.
You can check tutorials (if you think you're up to them, or just want to give them a try) at
Hawkee,
mIRC Scripts, and
mIRC.net
