I just remembered some other things....

Cedar and pine bedding is bad for them and can make them sick. If you use pine bedding make sure it is kiln dried.

Like guineapiggie said, fresh water should always be available. (I thought that was sort of a given. )

Two males that are not from the same litter will not always fight. Nutering a male will not change his behavior any. Two females may fight if they are not introduced correctly. (Same with males)