For formal meditation, you can use the seven points of Vairocana
THE 7-POINT POSTURE OF VAIROCANA
1. The legs should be crossed in the vajra or bodhisattva posture. (if you can't do that, just sit cross-legged in the standard way)
2. The hands should be folded, with your arms resting on your leg , the elbows slightly out. The thumbs should touch each other.
3. The back (i.e. from nape of neck to the small of the back) should be made as straight as possible – like an arrow or like a pile of coins.
4. The shoulders are held up and back (spread ‘like a vulture’)
5. The chin should be tucked in slightly, ‘like an iron hook’.
6. The tongue should be held against the upper palate.
7. The eyes should be open and relaxedly gazing past your nose's tip.
(there are some variations. you can close both hands around the thumb and place them on your knees.)
Most important is the posture of mind and speech. If you're doing shamatha for example, you should abstain from positive, negative or neutral thoughts and speech. If you're in a bus for example, you can always meditate even if you can't have a formal session if the right posture.
[I find these instructions for shamatha helpful, they come from Guru Rinpoche himself: en.chagdud.org/instructions-for-shamatha/]
--Karma Rigpe Wangchuk
"Meditation brings wisdom. Lack of meditation leaves ignorance. Know well what leads you forward and what holds you back."