Step 1: Realize that all the stories that are being told have already been told one way or another, and that some malcontent will attempt to find some obscure Jungian archetype to "prove" even the freshest story is some recycled cliche. Do not make any attempt to please such malcontents. They will not be pleased by anything other than you being as bitter and unproductive as they are. Top priority should be serving your story.
Step 2: You'll be spending a lot of time with your characters. Make sure you can stand them. Make sure the heroes are likable, but flawed enough to be interesting and leave room for character growth in either direction. Make the villains flawed enough to be villainous, but likable enough to be interesting, and again leave room for character growth. Whatever you do, however, don't make any of your characters too long-winded. More on that later.
Step 3: Story! Once you've got your characters, put them in place and give them something to do, somewhere to go. Plot, conflict, resolution should be simple enough, right?
Not really, but don't fret. If you're working with someone else's script, and they're any good as comic writers, you'll find that comic scripts make for terrible reading, but they should have all the description you'll need to draw what the writer envisions.
If, however, you're working with a story you've created, it's OK to keep your script a little more bare bones. You know what you want to do. You know how you want it to look on the page. And you can make your art show as much as you need of the setting, world building, and such, so there's no need to rewrite the Lord of the Rings.
Step 4: Now for the art. Besides using that to show what you shouldn't have to write, there are a couple of other tips to keep in mind. Make sure one panel leads to another in the order you want, and one page to the next, especially if you're doing traditional or traditional style comics. Even in web comics, you don't want a character or something in the background pointing away from where you want the eye to go. Arrange all caption boxes in order of how you want them read. If you don't read down up or right to left, don't arrange them that way. Same goes for word balloons. And position your characters accordingly. A character who speaks first should not be to the right of and below the character who speaks next. And, leading back to what I said about long-winded characters, make sure you leave enough room for lettering. And if you find you cannot make enough room, shorten whatever it is you have the character saying, or cut some words from the captions.
Step 5. More on lettering. You could have a great story and perfect pencils, but to tie it all together, the lettering has to look dynamic. Avoid type-style fonts except, say, when citing a typed document. However, it's most important that you keep the fonts you use neat and legible. Many a good comic has been ruined by unreadable lettering. (Including, I confess, an issue of one of my comics. Eep.)
