Summarize this article in one sentence.
If you have any friends who are interested in learning how to play guitar, offer to help them. This can be a way to develop your teaching skills and learn what methods are most effective.  If you're a reasonably good guitarist, chances are someone's already asked you to teach them. If not, ask some of your friends who don't know how to play guitar if they'd like to learn. Working with someone you know is helpful because they'll give you honest feedback on what's helping them and what's not. You'll also get a good idea of what kinds of information you need to know from your students. While you may already know these things from your friend, and have the ability to intuitively tailor a lesson to their interests, you can always reverse-engineer that to figure out what information you relied upon when formulating your lesson plans. Be careful not to lapse into a more friendly manner in these practice sessions. You can crack jokes or share stories, but keep in mind that you're trying to develop good teaching methods – not hang out with your friend. Once you feel confident enough in your teaching abilities to start looking for students publicly, spend some time evaluating the local market. You need to be able to price your lessons competitively.  If you set your rates too high, you'll have a hard time attracting students. On the other hand, setting rates too low means you won't be properly compensated for your time. Compare yourself to other instructors objectively, including relevant background and skill level. For example, as a beginning instructor you wouldn't want to charge as much as someone with 20 years experience or a college degree in music education. You also need to keep in mind the age range of students that you ideally want. This will impact the rates you charge as well as your advertising and marketing strategy. When you're just getting started teaching guitar, social media can be a good way to get the word out. Start a basic website and build connected social media accounts. Share the information with everyone you know.  You can build social media accounts without spending any money, which is part of what makes this a great way to spread the word about your services at the start. Later, you can decide if you want to spend money to promote your posts or create online advertising. Social media also helps you build your brand. Pick a name for your business and use the same user names on all websites. You may want to set up a discount system for those who find out about your lessons through social media, or who share your posts or make a referral. You also can create posts with a code for a free introductory lesson. Make sure when you craft the introductory lesson that the student will learn something right away and feel like they're advancing toward their goal of learning to play guitar in a positive and productive way. If you've decided you ultimately want to grow your business until you're teaching guitar full time, start small. Using word-of-mouth doesn't cost you any money, and can help you build a loyal following.  One way you can do this is by offering a discount for existing students who refer new students to you. After you've had a student for a month and they seem dedicated, remind them of the referral offer. They've had enough time with you by that point to know if they would recommend your services to others. Once you've had a little experience teaching a few students, you may want to start looking for other ways to find students, including directories and fliers in music stores or coffee shops.  Think about where people interested in music often congregate – this could include record stores and local music venues. Ask the owners if they have a bulletin board for advertising guitar instructor services. Schools also can be good places to advertise your services, particularly college campuses. You also can expand to online advertising, which can be a relatively inexpensive way to get the word out. Try to place advertisements with websites that cater to local or regional interests.

Summary:
Start by teaching friends for free. Research rates for guitar instruction locally. Establish a presence on social media. Rely on word-of-mouth at first. Expand to other methods of promotion.