Pretty much all expert meditators take the time to mention correct posture.
The rules seem to be pretty universal:
- wear loose clothing for comfort
- back straight – stops us from getting a bad back
- head straight – helps to keep us aware
- tongue behind the top teeth – makes us breath from our nostrils
- hands in lap or somewhere comfortable – avoids discomfort distractions
- there are as many ways of kneeling/sitting as there are meditators, personally I cross my legs though in the East, especially Zen, they tend to sit with their legs tucked under them
- it seems to be bad form to move around and adjust your posture in formal meditation sessions but I think it’s fine to move around a bit so long as you keep it to a minimum
- it is okay to sit in a chair but try not to get too comfortable or you might drift off to sleep.
- eyes either open and looking down, to try to avoid distractions, or eyes closed.