"Tell 'em they're humans from the home culture and that they can be fighter or a magic-user, pick one. If they say, "but I want to be a ...", make them that. Problem solved"
I think this should be applied on a much broader level than I suggested. Instead of the now-traditional "step one: select from this huge list of classes, step two: select from this huge list of races" (and step three being skills, step four feats in some systems,) I believe it's better to start with just a handful of choices, while being lenient when players have a clear idea about doing something different.
Limits and boundaries are good, if you can push against them. They inspire creativity.