A teacher is helpful in so many ways that aren’t immediately obvious, not just the “do this or do that” most people think of. My teacher has forced me to slow down and keep working at the same things until I get them - I mean, really get them, not just think I do. I am a very slow learner and the guitar is anything but natural to me but thanks to this I am finally able to start playing better than ever before.
If you can’t get a teacher I also recommend the method book “The Conservatory Tutor” by Larry MacDonald, (the same guy posting above
). I am near the end of Shearer’s first book and bought it to supplement what I have already learned. It is a very different approach and is full of gems (like a large section on segment practice) that I have found very helpful. The pictures and explanations of basic technique are very clear and he also works on musicianship right from the beginning. The books are only available through his website and, for the price of a lesson, I think would give a very good overview and reference even for someone who already plays other types of guitar.