The Silent Killer of all Electronic Equipment - D U S T!
One of the most overlooked subjects is proper care and cleaning of your rack and servers. Dust is very dangerous for all your equipment as it blocks proper air flow which can cause components to overheat and in time shorten equipment life spans. Definitely not what you want to hear when you have just invested in your total AV system.
The next time you hear a loud fan running from your components or dust accumulating on the equipment, cleaning is necessary. Our current project in Saskatoon is in construction phase and with all the drywall dust floating around it has us dusting twice a week! Thanks @Swiffer for making our life a little easier.