Step by step eh? Well talent, skill and imagination aside I've had to do this more than a few times, and will share what I know of the process in a nutshell. If there are terms here that I use and you need more information on - that's going to be more questions as I intend to be brief. This is a basic description - there are certainly more "advanced" techniques but I'm going to try and get you running "out of the box".
Now, the first thing you need is a story or script. You have to figure out how to start, where to go and how to end. You can't just start drawing a make it up as you go along.
Storyboarding helps at this point, it gives you an idea of how the project will look and how the action will flow from one scene to the next. Often you storyboard something and realize that you have too much focus on one event or you need an event as a "transition". Some people don't bother with storyboarding because it's time consuming but if I can help it, I work a storyboard up.
Preproduction should be drawing the characters - design them and make sure they have the look they need. It's also a good time to develop sets the characters will be in. If your characters are dark you don't want to put them are super dark backgrounds - they will get lost.
Production is the actual drawing. A traditional animation is 30 frames per second. This means if you cartoon is 5 minutes long you'll need 9000 frames of animation. Here's where software can help. You draw one background then draw your character on frame one - hold that drawing for a couple of frames then move them slightly and continue the process. Practice with stick figures and a "flip book" to truly get the feel of this process.
Once you have your thousands of images you feed them through a program like WMM and line them up 1-2-3-4-5-ect. Play the end result to make sure it flows right. If some action is too slow, you drop frames to speed it up or duplicate frames to slow it down a bit. Once you have your finished movie you can then go back and add music and the like.
