Judy, why not start by washing your ceiling with Dirtex and see what it looks like from there. We can't see it and you would get a better look also. This would be the way to begin any finishing project and you may not even need to do more. Years of chimney and cigarette smoke, for instance, can really add up.
I doubt that you really could use too much water on it and it probably would not bother the cedar if you did, but you might think about trying not to use more water than necessary. Let us know what it looks like when it has been washed and is dry.