Like any trade, guitar teachers who are just starting out make a host of mistakes as enumerated below. They are often engrossed in improving their skills more than imparting knowledge to others.
Most students stop seeing a guitar teacher because the instructor is likely showcasing how good he is with the instrument rather than helping the student to learn. Therefore, if you need to set up a guitar teaching business, concentrate on being a good teacher – it is not all about being a good musician. You can be a great instructor without being a great musician.
Mistakes all new guitar teachers make
Over-teaching
Sometimes new instructors feel obliged to be seen to be doing something to earn their fee throughout the hour especially when the student is paying by the hour. However, the best thing to do is to is to give the student time and space to internalize what you have requested them to do, to repeat what they’ve been taught, and to integrate it into their muscle-memory so that they eventually come on top of it.
All you need to do after giving just the right dose of instruction is to sit back, watch as the student grows through practice. Moreover, you need to show that you are patient enough and can wait as long as it might take till the student gets it right.
Failure to appreciate student learning rates
As any seasoned teacher would attest, there is a marked difference between the learning abilities of the different students who take up guitar lessons. Some students will quickly learn the tricks in just one single lesson, and there are others who will need continued drilling and repetition before they can finally internalize something.
It is a big 
mistake most instructors make to expect the same results from their students. Therefore, you shouldn’t make any assumption as to the rate of progress a learner will make. They are all unique, with different learning abilities. Be patient with each, and adapt to each of your student’s learning ability.
Failure to assess student ability
One of the cardinal sins that most guitar teachers make is to assume a learner has a certain ability or knows something without first assessing to ascertain if the assumptions are true. When a person approaches you for lessons, whether they claim that they are beginners, or intermediate, or advanced, spend the first 20 to 30 minutes assessing what they can and what they can’t do. The above are some mistakes all new guitar teachers make. In so doing, you can customize the lessons to be in line with the student’s ability.