Most of them are just common sense.
Config servers are critical to the health of your cluster. You MUST have 3 configuration servers in a sharded production environment. NEVER delete their data, always make sure you back them up frequently, and refer to them, if you can, by name using an /etc/hosts file (this will make your cluster more resilient).
Config servers are light processes but they must also live on 64-bit instances. Don’t put all 3 config servers in the same instance!
Original title and link: 10 MongoDB Tips From Engine Yard Data Team ( ©myNoSQL)