oiboy. if you already worked for a company, see how they advertised.
it depends on your area, but you can do door to door, talking to people and passing out flyers. There is a service called every door direct mail from USPS but its obviously more costly. about $.15/ flyer and they mail it out to a zip code and mail route on that zip. there are a number of specific requirements for your flyers design and layout for it to be elligable. You also must go to the specific post office the route is and drop them off. they must be a certain size and in bundles of 50. some of the flyer sites will do this stuff for you for more money.
craigslist can work well too depending on your area.