Every printer I've ever had comes with a user guide which describes trouble shooting as well as cleaning procedures, how to replace the ink/toner, etc. Have you read yours? If you've lost it, you can in all likelihood go to the HP web site and download it. Contrary to what some people seem to think, reading the user guide won't give you leprosy.
Printer is placing the same "smug" marks on each page it prints? How can this be cleaned?