In this section we are less concerned with technique than we are in building a relaxed, efficient approach to your instrument. You'll need to use the skills developed from relaxation exercises to adjust the way your body wraps itself around your guitar. You need to be conscious of both your own body and its physical relationship with a static object. The interaction between the two of you is more important than where you put your hand or whether you sit or stand.
That interaction is however a personal one, between you and your guitar not something that can be formulated and presented here in six easy to follow steps. For that reason you're being presented here with a process, not a solution. I don't know your solution but I've got a good idea of how you can find it for yourself. I'll make recommendations, feel free to reject them, ask yourself before you do though a few simple questions.
Learning to relax into a sound posture happens slowly, by degrees. You don't need to arrive at an optimum posture before you start to notice results however, that will happen surprisingly quickly and you'll continue to improve the more you're able to put a few basic concepts into practice.
The rest of this section can be divided into analyses of the upper and lower body positions. The essence of any sound posture depends on a stable base and a relaxed, adaptable upper body. Both the sitting and standing postures will provide that base so the descriptions of the shoulder and arm positions will be equally relevant in both instances.