A lot depends on the model of the printer.
Most newer HP laserjets require LITTLE or NO maintenance, other than once every 3 months or so, or at every toner change, whichever is the most frequent, using a fairly powerful vacumn with a fine nozzel and soft brush.
Open the printer, remove the toner cartridge, and vacumn out any paper dust and residue which may have accumulated. Vacumn the fan(s) and ventilation openings.
Examine the Toner cartridge(s) and drum unit if any for signs ofdamage.
Don't force the toner cartridge down to it's last gasp after getting low toner warnings.
Color laserjets require a more through cleaning around the toner cartridges, and those you'll have to remove 1 by 1 and clean throughly, including the cartridge itself.
You no longer have to worry about corona wires and fuser guides.
If you do have an older laserjet with coronas and fuser guides, clean all the above as described, replace the fuser guide at least bi-annually, and gently wipe the corona wire with a soft brush at least every 3 months or toner cartridge change.
Don't shake the toner cartridges vigorously, but a gentle side by side motion will settle the toner and extend the life of the cartridge. Avoid touching the interior components of the drum unit and toner cartridge. Avoid exposing the drum unit to prolonged light.
After cleaning, do a couple of self tests to pick up any residual toner which might have beens stirred up while cleaning.
