as long as there's at least 45-60 minutes between flights your luggage should be fine - it's your person you have to make sure gets to the connecting flight... the MIA international terminal is large, they've done some renovations and now there are two different international terminal locations, so it's possible that the distances between domestic and int'l flights can be a bit of a walk, depending on which terminal you're flying from/to. And the airport is not well marked, it can easily be confusing if you're not prepared.

so i would make the suggestion that you find out from the airline what gate (or at least which terminal) your domestic flight arrives to, and what gate/terminal your connecting flight departs from - then go online and look at the MIA airport map, that way you'll be better prepared & know exactly where you'll be going between flights once you get there.