Gracefaerie patterns has a sizing chart -- she tells you the exact model of doll and basic measurements each pattern was designed for, and some of the patterns are available for more than one size/build of doll.
http://www.gracefaerie.com/patterns/sizing.html Some patterns I've gotten have separate pieces marked distinctly for "Obitsu" or "Rainy" or "AoD" or "Lishe" -- usually pieces that are more fitted. Skirt yokes that accommodate the waist/hip measurements are where this comes in useful, because that's one place these girls do have a range of size/proportions.
Ditto what K2! said about shoes, and checking inside length -- it will save you a lot of annoyances!
Fortunately a lot of outfits are forgiving -- but if you're thinking of something fitted, like a corset or jeans, etc., that isn't basically stretchy -- check measurements or wait until you have the doll (She can always wear something looser at first...)