You can find articles and tips for maintaining your push lawn mower in many different places on the Internet. Some of these articles are helpful, and others are just space-fillers. SouthernStates.com has a good article on how to tune up your lawn mower, including an easy way to sharpen the blades, and it gives you the best order to do things in to save time.
The only drawback to this article is that it only discusses push mowers with sponge air filters. If your mower has a pleated (paper) air filter instead of a sponge filter, disregard the section on cleaning the air filter. You can find a great article on replacing lawn mower air filters, and a breakdown of the different kinds of filters at JacksSmallEngines.com.