Printer Maintenance

I am creating a pirnter maintinance schedule for 21 HP LaserJet printers. I am looking for information of proper procedures on manually cleaning, and preventative maintenance.
HP keeps telling me to refer to my manuals for cleaning information, however all it describes there is how to clean the ‘feed guides’ and not the entire printer.
HP cleaning kits are available, but with this many computers, being used this often the expense would be to great.
Any information available?