Every comic book writer brings their own format and style to the task. Here's examples from some of the top names showing how they do it, including a Neil Gaiman script for Miracleman, a drawn script by Jeff Smith, a Jay & Silent Bob comic book script by filmmaker Kevin Smith, a script for Marvel's Deathlok from Milestone Media cofounder Dwayne McDuffie, a plot from Blade and Cyborg co-creator Marv Wolfman, a GoGirl! script by Eisner Hall Of Famer Trina Robbins, a Greg Rucka script from the Eisner Award-winning Whiteout: Melt, and a script by Eisner Award nominee Nat Gertler paired with the finished art by Eisner winner Steve Lieber.
These sample scripts make a great resource for aspiring comic writers to learn from, for aspiring artists to learn what to expect, and for those who are just curious about how it's done.

Anything you've ever wanted to know about comic scriptwriting is in here -- Savant

It's an attractive package put together by comics writer Nat Gertler, and it's welcome, indeed. GRADE: A -- Comics Buyer's Guide

There aren't many books that pass for "invaluable references" in our field, but this qualifies. -- Steven Grant's Permanent Damage