The short answer to the question as to how to hold a guitar properly is as simple as: there actually is no such thing as the one and only way to hold your instrument in the right fashion. It ultimately comes down to two things: you need to be comfortable and you need to insure that whatever position you choose allows you to play over longer stretches of time without getting tired too soon. Or even worse, possibly ending up with a twitch in your back or neck.
Alright, in the video below I show you a number of factors that you may want to consider to figure out your own personal preference when it comes to holding a guitar:
In the last part of this demonstration I showed you the typical approach used by classical guitarists. I personally came to like this position a lot, even when I practice with my electrical guitars. It allows me to keep my upper body straight and I have a great view on the fretboard. However, it also means in almost all situations that I need to have something to elevate my leg, otherwise it just doesn’t work. Since we are on that point, you may want to check out my post “How to use a guitar foot rest”.
With regard to using a mirror; as I mentioned in the video, you have to find out for yourself. Some of my students feel that it helps them tremendously as they practice guitar, others find it way too distracting. So you just try it out and see if it works for you. Or use a camera with an internal or external screen. That way you can record yourself which has many advantages. First of all, you can see and hear yourself playing which gives you the opportunity to work on things that need further improvement. On top of that, you will see exactly what position you’re in. That can perhaps help you to find out why you are getting physically tired prematurely whenever you practice. Because these things are not obvious while you are actually in the process of playing – only later, when you see yourself on tape you might say: wow, look how much I’m twisting my back.
So, in sum, how to hold a guitar properly cannot be answered in only way particular way. Try a few different things as described in the video. If you get tired quickly, that’s usually indicative of you not holding your guitar in ‘the right’ way. Try a guitar foot rest or sitting in a different chair. Usually, a small change like that can make a huge difference.