I am a mural artist myself and I've never painted a ceiling either, but I do have some suggestions for you.
1) Scaffolding is a must! You should also have all your paints at hand. Use a palate. If you don't have a palate, you can use disposable styrofoam plates. They work just fine for smaller projects. If you are creating a large mural, you can make your own palate out of a piece of cardboard. Yes, I said cardboard! When you're finished, you just toss it. No clean up there! If you are mixing paint that you want to save later on (maybe for touch-up)you can store it in those ziplock tupperware containers. I know it sounds crazy, but I've done it this way and it saves me time and clean up.
2) In order to actually paint on a ceiling, it is best to first get a feel for the scaffolding. Once you are comfortable working at that height, you should not have any problems. Bring a pillow or pad. You are going to need to lie down while painting. You want to feel comfortable while you are lying in that position painting for hours at a time.
3) Transfer paper is a good way to mark the ceiling for the mural, rather than doing it freehand. Take your original drawing and make a grid. Enlarge the drawing to fit to actual size and then transpose it onto the ceiling. It sounds difficult and it will be for the beginner, but once you've done five or so, you'll be adjusted to it.
If you have anymore questions, feel free to ask.