For traditional cheese fondue, the only real rules are: USE GOOD CHEESE. The best you can find. After all, that's the whole point of the dish.
I usually use a mixture of gruyere and emmenthal or maybe jarlsberg -- traditional swiss cheeses (I know, I know ... Jarlsberg is Norwegien but I like it).
Of course you can use lots of other types -- just make sure it is a good melting cheese (ie, no parmesan)
The other rule is not to omit the wine, as it is what helps prevent the cheese from curdling.