Once the guitar is in a decent position and stability is sorted, the position of the hands needs to be addressed.
We have to work within the limitations of our hands and fingers, especially when it comes to our wrists. Play with a bent wrist and the fingers won’t move easily - this is one of the most important points to remember. I was taught to play with a bit of a bent wrist for the right hand, like lots of people back in the day, perhaps something to do with tone; it looks awkward and it is awkward. Playing becomes an uphill struggle, the fingers just won’t move easily. The straight wrist approach has to be adopted for the left hand too, if it isn’t, stretches and rapid movements won’t be possible. More importantly, playing with bent wrists could result in carpal tunnel related problems, so good advice (even when playing with straight wrists) is to take regular breaks when playing and also to practise stretching exercises away from the guitar.
When playing the guitar our focus is on the notes to be sounded, but we mustn’t forget the position of our thumbs, particularly the left hand thumb. It can give stability to the hand and guide the hand when shifting. The video explains how it can help or hinder our playing.
Which leads on to the importance of anchoring our fingers of both hands wherever possible. Left hand: leaving a finger on can make life easier for the other fingers, as long as it doesn’t have an impact on the harmonies - not many actively promote this approach, which is a shame as it really helps with a solid hand. The difficulty is that the finger to anchor changes depending on the context and must be decided 'off the cuff’ (I eventually annotate the score where relevant though).
Anchoring the right hand is pretty straightforward in comparison: if the thumb is playing, anchor the fingers on the first string and if the fingers are playing, anchor the thumb on a string two or three strings lower. You may ask about anchoring the little finger on the soundboard… this is discussed in the video. The important thing to remember is that the anchoring is there to aid the movement of our fingers and as soon as the anchoring creates tension in the hand, it isn’t helpful, rather the opposite.
Lots of guitarists will say they do what’s right for them, but there are certain ways the hands function to enable freedom of movement that we have to work within. You’d think it was the guitar world’s biggest secret given the range of approaches guitarists take - a major misconception is that these principles are reserved for the classical player, but if you look at the best players in any style, they all play with straight wrists and anchor well.