This is how I do it:
1. Come up with completely stupid idea
2. Decide "HEY, I MIGHT JUST ANIMATE DAT SHIIIT"
3. Write out a very basic storyboard and script (it basically just looks like a little comic in my notepads)
4. Voicework and background music/sfx
5. ANIMAAAAATE DAT SHIIIIT
6. Cry when its done
In terms of the order of how I animate, I draw the backgrounds first, overlay the character, then do lip syncing.