i've always booked Select fare so i can choose where my Cabin is, go on Cruise Mapper note what cabins i would like ,check what is above and below them then phone and see what's available.
Always got the one i wanted apart from a couple of Cruises where none were Available for the ones i wanted but just booked a different Cruise with them.
Going on 3 Cruises next year and got the Cabins i want.