Major typically indicates which driver the device uses. This is typically somewhat arbitrary and has a lot to do with the order in which the devices were added to the system.
Minor is the way devices are subset within the driver and varies by the type of device. They can be as simple as order (01, 02, 03, 04) or have complex meanings (e.g. Serial ports minors in a certain range might mean "software flow control" indicating they're used for terminals or "hardware flow control" indicating they're used for modems)