I use real-world titles– priest, queen, e.t.c.– except where there is no close equivalent in my made-up society. I find this is rarely the case, as most of those titles can mean a lot of different things anyway.
I do avoid ones with more specific meanings, like 'bishop' or 'duke', as they would have false associations. If I need to show gradations of rank, I give characters flowery job descriptions ("High Priest so-and-and, Guardian of the Sacred Flame").
Basically, my rule-of-thumb is "don't confuse the reader more than you have to".