as a guitar teacher myself, i remember what it was like when i started out.
the easiest way to do it is seeing if you can get a job at the local music store. they'll take a cut for letting you teach the lessons there, but chances are its WELL worth it. for one, when people want lessons, they're more likely to call a store than just some random person. plus, nobody has to know where you live, and you dont need to drive from home to home. usually the store will have a policy for lessons, so you'll always get paid and they'll typically take care of the people that sign up, and they'll make sure the people are paid up too. when you teach on your own, its really a pain when people can only pay by cash or check, and if someone "forgets" their money, or doesnt want to pay for a lesson they didnt show up to, or a check bounces, it can be a real burden. ALSO, you might get a pretty nice discount if you teach at the store. its just really hard to compete with the music store gig.
but, if you dont wanna teach at a store, you should take out an ad in the paper, put up a craigslist add every few weeks, keep a website open for your schedule, put out flyers at schools and places where kids go (most students are usually kids, but sometimes adults sign up too).
you can make it work out either way, but the music store thing is usually WAY easier.