Great Teachers Vs. Great Players
There are millions of teachers out there. Like mechanics and doctors, there are bad ones, mediocre ones and great ones. You might venture out looking for a teacher and find one right off the bat. More than likely though, you'll end up going through a couple of different teachers before you find one you really like. This isn't necessarily a bad thing since every musician has their own approach and something can usually be gleaned from their experiences. However, when you find the right teacher, you save yourself alot of time (and money) because you focus on the essentials, ans get right to the heart of your particular matter without wasting your time working on things that don't brigng you closer to your goals. As confusing as it may sound, the most successful musicians don't always make the best teachers. Sometimes you'll go out and see a great performer and find that they give lessons only to find that you didn't learn that much from them. Teaching is a whole other skill and just because you find a good player or good performer, that doesn't mean they'll be a great teacher. Being a good teacher is all about communication. It means being able to explain different concepts clearly. It's being able to see what you need and what you don't need. It means paying attention to your development and making sure you're heading in the right direction. Great players don't necessarily always have these skills. Also being a good teacher means being well versed in all aspects of music. Sometimes you'll come across a great (for example) blues musician and want to take lessons from them. That's great if you want to concentrate on playing that specific music. But, if want a more complete program, make sure the musician knows all of the other aspects like good technique, music theory and the fundamentals. It's possible to be able to play many different styles without having a clue about what you're doing.
Background
Teaching in itself is a talent and takes a special kind of person to do it really well. There are a number of things that a teacher must do that aren't part of the normal musician's skill set. Some of these things include 1) putting together a program for each individual student. 2) monitoring the students progress and making sure that the right things are being worked on. 3) figuring out what the student needs and their strengths and weaknesses.4) including all of the necessary fundamentals and not just 'learning tunes' or 'licks'. There are some teachers that go through school and have degrees from accredited colleges. While not a guarantee that they'll turn out to be a great teacher, it's a good indication that they've gone through numerous programs and have a well rounded knowledge of music fundamentals. You can go through private lessons or go down to your local music school and see what they have to offer. Generally, the 'best' teachers will offer private lessons because they've usually been doing it a while and have worked up to making enough money just from private students. However, this isn't always the case. Most teachers I know teach at a school and privately. Many fine teachers can be found at the music schools. Most music schools require that the instructors have a music degree. Make sure ask. Talk to the people at the school about where you are and what you want to learn. If you're more advanced, tell them. Some schools have specific teachers that will take on the more advanced students or students that have specific requirements (e.g classical or jazz guitar).
Know Thyself
It's important to know what you want from the teacher before you even start. Most good teachers will ask about your goals are right off, but now always. Make sure you know what you want and make sure to tell them. Even if you're just starting and don't know exactly what you want, simply state that you want to learn the fundamentals, proper technique and some songs in your favorite style of music. That should be enough to let any teacher know what to do. If you're more advanced, tell the teacher where you are, what to want to learn and what you expect from the lessons. The more information you bring to the teacher, the better. If you've had any bad experiences in the past, let them know that too.
What Can You Do For Me?
Once you've found a teacher, ask them what they teach, how they go about the lessons and if they follow any specific program. Most teachers have a preferred way of teaching. They may not always have a developed program written out but they do have a specific way of teaching. Ask them about this beforehand. Ask them what you'll be doing for the first 6 months. As soon as they see where you are in your development, they should be able to answer this question. Be prepared for any answer they give you. Sometimes I come across a student who wants to learn it all, right away. Once I tell them that it will probably take the better part of a year (and more!!) to learn the skills they want to develop, they don't always react positively.
Never Stop Learning
The biggest advice I can give about finding a teacher is always challenge your teacher and not settle. Don't be afraid to challenge your teacher. Quite often students will go out and just settle with the first teacher they find. You usually end up creating a relationship with that person and will stick with them. This isn't always in your best interest. Once you find someone, make sure that you're learning and heading in the direction you want. Keep your ears and eyes open. If you have a chance to do a lesson with another teacher, do it. See how that lesson goes. Compare it to your current teacher. You'll find that you'll learn something from every musician you come across but then there will be that one that you come across that takes your playing to a whole new level.