For most of our practice, we will be sitting down, & there are some important considerations to make while sitting. We encourage you to practice standing now & then to get used to using a strap. When we go to jam with others, standing may be necessary. For certain types of playing, sitting is the primary way to go [i.e. Classical, Fingerstyle].
We work with 3 points contact when sitting: leg/s, forearm, and chest. We find balance within this cradle.
There are many ways to sit with a guitar (footstool, cross-legged, etc.), and we recommend that you simply get comfortable. When we are aware of our body while playing [not just our hands], it will be easy to detect when there could be a problem. The main question will be: “Am I comfortable?”. Emulate your favorite players.
Another piece of comfort is having everything in our practice space within arm’s and foot’s reach. We arrange our practice space so that we don’t have to get up to change aspects of our practice environment.
Guitarists can end up suffering with back problems. With proper alignment while practicing & a good stretching ritual to get things going, it is possible to avoid common body problems. The main consideration throughout our playing life is our posture. Pay attention and settle in.
Some low impact exercise ideas to check into: Alexander Technique on Wiki, Yoga (Sun Salutations – I do this sequence as often as possible, along with push-ups for an ‘absolute bare minimum’ for working out), Fulford exercises, & basic stretching.