Disney’s Clay Kaytis wrote a letter containing his 2D animation process while working on Treasure Planet. A few great tips from it would include:
Work fast and loose in the beginning; just worry about getting the animation right.
For every change – be it arc, expression, squash, stretch – DRAW IT.
Staying loose, get caught up in the rapid creative time of the scene. Do not stop until you have said everything.
Although the letter alone gives awesome advice, Clay responds in the comments below with his ENTIRE CG ANIMATION WORKFLOW! Follow the link to see it yourself.