First of all,you need to make sure it doesn't contain asbestos or lead.
Afterwards, if the ceiling has not been painted with oil paint. Spray a patch with water, and scrape it with a putty/ other wide knife. Try not to do it on too much of an angle, so that you don't gouge the drywall/tape.
Some people cover the whole room in dropcloths first, and scrape big passes and let everything fall. I find it leaves a bigger mess, and the dust eventually settles, (no matter how you hard you try to avoid it) in your vent system.
I prefer to use warm water, and I go on a step ladder, and use a box lid to catch the fallout. I do small patches at a time.
I too did the dropcloth thing, and bought the specialized scraper with a bag holder. It was a waste of money. After a few passes it left gaps, the bag would sometimes fall, and it got very heavy.
This is what works best for me, and it is much easier on my shoulders. I have done this a few times, and I find it leaves less damage = less repairs later. It also helps me control the dust, which is a definite bonus.
You're welcome. Have fun.