Matt Fraction considers the art of writing a comic:
i think every writer has to find how they write their scripts, and they have to find how they write their scripts for their artist. these are two wildly different things. Alan Moore and Neil Gaiman are the best thing to happen to comics writing and the worst things to happen to comics writers because their styles of script writing, so legendary as to become apocryphal and for the longest time the only printed examples of comics scripts one could find, made generations of kids write terrible sub-Alan Moore and terrible sub-Neil Gaiman scripts. The lesson is, of course, don’t write like Alan Moore or Neil Gaiman; write until you figure out how to write like you.The only way i’ve found to know how many pages a scene needs is to write until it’s right. That’s why i tend to start with lists, working like very loose outlines. it gives me a rough breakdown of the mission each page has in the greater whole but keeps things loose enough that i can reshuffle and rework quickly.
More at the link.