The way I did it was to first of all, sit down and work out what images I needed - characters, backgrounds, objects etc. Then I drew them. On paper, that is. Once I’d got them all together, I could scan these doodles and import them into Flash. I traced over them and coloured them in, then deleted the imported gifs.
Then I figured, if we want these characters to move and talk, then they have to be divided up a bit. So I separated things like eyes, mouth and hands and them into their own symbols. I also drew some different poses and positions for each of these objects. Things like mouth open, closed, surprised looking… That kind of thing.
Once I’d got all the images together that I needed, I made some small movie clips of what were going to be common actions, such as talking. So for each persons’ mouth, I made a small, roughly 5 frame loop of all his / her mouth positions. When you run that, it looks like they’re talking.
Any transitions that need to be made, like fading backgrounds in or out, I made movie clips for as well.
Then it was simply a case of making a whole new movie clip per scene of the cartoon. Layers for scripting, backgrounds, characters, sound (if applicable). Put them all together with a final few bits of scripting, and you have a finished cartoon.
So that’s how I did it. It is a lengthy process, but well worth it when you see your finished animation.
I’ve written a tutorial on kirupa for tracing images into line art for Flash. It’s in Flash MX - Special Effects - Drawing Line Art or something similar. It’s in the Flash MX section, but the process is identical for Flash 5.