Of the six preliminaries undertaken prior to contemplation, the fourth is to take the eight-featured sitting position and to set one’s motivation.
How we sit is very important. Partly this is because bodily posture will affect the intensity of one’s mental alertness. But this is only the surface explanation. In metaphysical terms, we are told that it affects one’s state of consciousness even at its most subtle levels. In short, our contemplation will be far better focused if we assume the traditional erect sitting posture than if we slouch or lie down. Without good focus and alertness, our efforts at visualization, analysis and the cultivation of virtue will amount to little more than daydreaming.
The correct posture for Lamrim meditation described below is known as the eight-featured sitting pose of Vairocana. Let us take it point by point.
Cushion: Tibetans traditionally use only one cushion. I do not know if they give it a special name. But we Westerners usually employ the Japanese term "zabuton." Tibetan texts say one should have it raised slightly at the rear. This will keep the back straighter by making you roll your hips somewhat forward. The purpose is to stave off muscle fatigue by shifting weight more toward the bony part of the pelvis and away from the muscle of the buttocks. Commonly, most Westerners follow the Japanese example of employing a second, smaller cushion (called a "zafu") toward this same end. (Pun intended.) It works out pretty much the same.
Also... In placing the cushion, don’t just toss it down on the floor. Evoke the same sense of reverence in this that you have for the other parts of the rite. Do so mindfully.
Legs: The legs should be crossed. Full vajra (lotus) pose is not a requirement for Lamrim. Here we may choose to sit with the legs in half-vajra or even just crossed in the ordinary way. But if one has plans to eventually engage in Tantra, then it might be well to start getting used to full lotus now; because for the completion stage of Tantra, this much more difficult posture will be a requirement. So if you can, do. But don’t let physical discomfort distract you from your contemplation during Lamrim. Rather than that, consider working up to full lotus at a less critical time -- like in front of television, when the reverse will be true; when it will be the program which draws your mind away from the discomfort.
Note: If you have some medical condition disallows certain features of this posture, that is of course a legitimate exception. All that is absolutely required is that each practitioner should strive as best as they can.
Hands: Place both together in the lap, palms up. Put the right hand on the left palm with the thumbs touching lightly. Do not rest them on the knees for Lamrim, as the above position has symbolic meaning. It is a special mudra representing wisdom conjoined with compassion.
Back: Keep it straight, but not streached tight like a piano wire about to break. Allow the vertabrae to rest gently like a stack of coins. There will be some very slight s-curvature as is natural to the spine. But don’t let yourself slump into a c-shape or question mark. As a rule, do not allow any posture which would collapse if modeled out of stacked coins.
Mouth: Lips are best kept either lightly closed or very slightly parted -- whichever way feels most natural. Allow the teeth to touch lightly. Don’t clench. And let the tip of the tongue rest lightly against the palate. Don’t press. This prevents both drooling excessive thirst.
Head: Incline the head slightly forward. Just a few degrees. Be light about it. Be alert not to stiffen the neck muscles. Stay relaxed.
Eyes: It is best to keep the eyes downcast and slightly open. About half closed over the pupils works nicely. Closed enough to prevent you from focusing on external objects, but open enough to let in some light. (I have read in a scientific journal that the color and intensity of light entering the eye is a prime factor in rousing the brain to wakefulness.) Incline the eyes downward just enough so that either side of the nose falls at least partly within your peripheral vision. And if you wish, cross them slightly to help defocus distracting objects in front of you. If even this does not suffice, it may prove necessary to face a blank wall.
Note: Beginning meditators often have trouble with this. So if keeping the eyes open poses too great a distraction, you may do better at first by letting them close very lightly. But do try and work up to the recommended practice as this definitely helps to stave off daydreaming and drowsiness. At the opposite extreme, keeping them wide open will excite and distract, pulling one’s mind away from the task at hand.
Shoulders: Keep them level and relaxed. To stave of slouching as a prevention against torpor and sleepiness, try holding the shoulders level and slightly rearward, adjusting the elbows accordingly. Never hunch upward, as this is will likely bring on a killer headache in short order.
Breath: We ordinary beings cannot easily hold two things in mind at once. And since the next step will be to evoke a virtuous frame of mind, it is important to first purge ourselves of all negative thoughts and emotions. This is more easily accomplished by first concentrating on something neutral as a preliminary step. The breath is about as neutral an object of focus as we can find, and something which we always have with us. What is more, by attending to the breath we can obtain a good measure of our emotive state. When the breath is calm and regular, that is a good sign. Here we do not wrestle for conscious control over our breathing. Rather, we just observe and keep count -- without employing rosary beads to keep track. We don’t breathe deliberately. We just breathe naturally, while observing mindfully and keeping count mentally. If we lose count, then we just start over. There’s no fixed goal to count up to. Just count as many as you need to assure complete neutrality of mind. As a general rule, beginners should count to at least twenty-one. If it takes until one hundred, that’s okay. The whole time just breathe, observe, and remember the count. Try not to employ mental props to help keep count -- try not to narrate subvocally or picture an imaginary counter. There’s no need to visualize numerals ticking off numerals one by one, or to hear your mind’s voice call out, "In and out makes twenty." Just breath normally and maintain awareness of the count mentally. Merely observe -- in, out, nineteen... Your normal breathing should not change. The only difference should be that you are now aware of it. Then, as soon as neutrality of mind has been achieved, let go of the need to count any further.