(Long post ahead, summary at the end!)
I will argue vehemently with anyone who tells me the only good way to write is by planning, outlining, or writing huge panels of background on everything and anything before starting to write.
No, the people who claim that--you guys--you might be right for you but there's aproximately a 50/50 split between the writers who plan and the writers who don't.
This is why.
On the other hand, I'd like to warn against too much planning. I've fallen into this trap, and I have a friend who, in the short time I've known him, has exquisitely planned out a million different projects and not begun a single one.
At a certain point, you have to stop yourself, and just pick up the damn pen/mouse/pencil and GO.
Said perfectly, though I disagree with other things said--and I'm a writer first, artist second. Overplanning kills. What I disagree with is this.
Not planning for the future of the plot is an excellent recipe for writer's block.
Not for everyone. Meet ME! Tiana! Who only really suffers writers block if she knows what's going to happen. This causes slightly remote problems with her writing because she can't preplan fics or anything, she has to write without much of an idea of what's going to happen. Seat of the pants writer, and she's not wrong, she's just one of many writers who writes this way. Nanowrimo is her muse, a month of frantic, and supposedly bad writing, the best way she's found to produce anything. If she wants to write something long, she waits til November and finds that, with a crappy start comes an amazing story. She realizes not many people can write like her... not many people can jump into a story with no idea of setting, characters, or plot, and produce from beginning to end a novel that makes some remote sense to other people, and in a month make it readable... but she winces every time someone says 'but you can't write that way!'
Because she does.
Hence my tip for writing: there are no rules for writing. Find what works for you. Find what inspires you to go and don't decide 'but since all these other people write like this, I should be too' and kill your muse. Find something that works. If that's 50 pages of background material, maps and details and drawings and everything... then whatever, do that. If you're like me, and that's 30 days of manical writing at top speed to produce over 100k and a nearly finished novel, hey. And if you need a background wiki, hey, that's fine too.
Find what works to keep you writing.
And then, tip number two.
Look, maybe you're writing a novel. Great. Finish it before you edit it. Maybe you're writing a script, as mentioned here. Finish it! You can work off an outline, or you can write the whole thing first. I have a single draft of my webcomic script, nearly finished, with an outline to the end. I'm editing it as I draw. It works for me. I wrote the thing in a month for ScriptFrenzy, it's surprisingly coherent for all that and where things need to be changed, I'm changing in the rough pencils and changing as necessary as I carry through the art.
The only preplanning I do now is generally in my head. I'll take NOTES, that's it. I have all these scribbled bits of notes and backgrounds, but nothing really 'readable'. I keep Notepad files on my desktop to drop these things in. For the original writing, I might start with a few pictures, and then write from there. Things can evolve as I go.
For comic writing, find a way that works. Maybe you'll want to write from narrative, maybe you'll want a TV script, whatever. Mine's formatted roughly like a movie script with excess description of emotions and blah. I would highly suggest finding what works best for you as an artist.
And then, if you're writing, write ahead! You don't need to finish, though I'd advocate it, just write ahead. Have an outline to the end, at least, so you're not bouncing around. Writing from the seat of your pants ONLY works in novel format... in comic, remember, you can't go back and edit once you've drawn, so you want all the plot devices planted ahead of time. If you hate outlines to death, at least have a list of plot things to plant and stuff.
For a gag a day strip, I suspect it'd work differently. I think for 'yay, serious stuff'.
No jokes in my brain, not so much.
And don't sacrifice characterization for jokes. I hate that. I think a lot of readers hate that.
And, as mentioned once before. LISTEN TO YOUR CHARACTERS, THEY ARE SMARTER THAN YOU SOMETIMES AND CAN DO AWESOMELY HORRIBLE THINGS.
Of course, you can always drop them into acid if their ideas are... ahem. Yeah. Let your characters come to life in your mind. It's nothing to be afraid of. Let it happen!
Meh, almost done rambling. I leave you with one more writing tip.
"WHO is doing WHAT to WHOM and WHY THE HELL SHOULD I CARE? What is it, and why should I care?"
It was the best description of a query letter (thank Miss Snark) I ever read, I wrote it out and stuck it on my whiteboard as well as a few notes on a couple other things.
And that's the base of a plot. It might come out to be more than that. Who might be more than one person. There might be several whats. In my case, I might go (omg spoiler) 'Mysada is haunting Dreshae, trying to use him to regain her body' for one of my lines of plot, which is one out of a few that interwind, but each one of these I can summarize into a sentence or two. You need to be able to summarize the motive of your characters, and what they're doing, in not that many words. If you can't, it's probably too complex--or lacking a plot, there's a difference between plot and concept. Concept is a WHAT.
Plot is a why or a how.
Concept is 'Elves are trying to take over the world'.
Plot is "The only way to stop them is to build a portal between worlds and drive them into the abyss!"
But yeah, basically...
1) Find a way that works for you.
2) WRITE!!! Don't get caught up outlining or editing to death!
3) Let your characters write for you.
4) Make sure you have a clear grasp of your plot and concept before you try to draw it.
5) Because these are what you're going to be using to hook readers.
I consider myself a better writer than an artist.