DO NOT let your tank water enter your eyes *ouch*
DO NOT smell your live rock to determine if your tank is cycled.
DO NOT taste your tank water to determine the salinity level.
DO NOT leave dead fishes (if any) in your tank, thinking that your cleanup crew will take care of it, especially the bigger ones. Take it out immediately.
DO NOT think that your cleanup crew only eat fishes' waste.
DO NOT forget to head count your fishes every feeding time and assess their health.
DO NOT place your face too near the tank and stare at it for hours!