The site thinks that you are a spammer from the username being used. This is all that I can think of to get an answer to your question.
If you want the outcome to look really great, you start off by washing the ceiling. Not a pressure wash, just a good wash with water. That will also help in removing some of the loose paint. Then you can either scrape or sand the entire ceiling. I would sand it. After is it sanded, fill in any of the large gaps and cracks with a good quality wood putty. You can now either hose it off once again, or wipe it down with a damp cloth. Let it dry really well. Then apply a high quality oil based primer, maybe even a couple coats, and then a couple coats of high quality oil based paint. I would go with a pale, sky blue. This is an old wives tale about painting the porch ceiling sky blue. Some say it will keep the bugs away, some say it keeps the spitits away.
If you follow those steps, you will probably not have to ever paint it again. Take your time in the prep work. The painting will be the quickest step.
Handy Andy In Mt Airy NC