Worried...

Watchmen, Maus, Alex, the first dozen issues of TMNT, Frank Miller's entire back-catalogue, Hellboy, ElfQuest, Tintin, Den (or any early Corben), some Manara stuff (pick one at random), Fritz the Cat, the Lee/Kirby FF, Ditko-era Spider-Man, sixties Gold Key comics (Turok and / or Dagar: Brothers Of The Spear), Alan Moore's League Of Extraordinary Gentlemen...

I could be here all night making an essentials list.

Ask the artist how he prefers to work...the outline method, full script or thumbnails/breakdowns.

Learn to write a great comic by reading the best that has been created. Any moron can look at a crap comic and think they can do better, but the real challenge lies in looking at something brilliant and saying "I can do better." It's an egotistical thing as much as a confidence-building excercise.

If you really need a nudge...

There's an old Stan Lee & Steve Ditko Guide To Writing or Guide To Drawing The Marvel Way, or something like that (looked at it once and decided it wasn't for me). Scott McCloud's Understanding Comics is handy, and I would suggest you look at the numerous 'behind the scenes' extras that have been published in Wizard, Comics International, Comics World, et al.

Some artists like Alan Moore-type novellas to land on their desk (figuratively speaking), while I kinda like neatness and brevity if there is no need for massive detail.

Which genre are you writing?

You're thinking of 1978's How To Draw Comics The Marvel Way...by Stan Lee and John Buscema. Although the book is something of a classic, it's geared toward artists, not writers.

I think the best guide to writing comics or the "graphic narrative" that has come out recently is The Everything Guide to Writing Graphic Novels...but then...I would say that.