I’d probably read the Yoga Sutras at least three times before the significance of samyama dawned on me: this is how meditation works. This is what we’re doing every time we sit. I found it phenomenally helpful in understanding my own experience and hope you do to.
On posture: first of all, sit up. This activates the brain in a way that reclining turns off. Secondly, relax your face and shoulders and slightly tuck your chin. If you find your brow knitted, your jaw clenched, or your chin lifting, reset.
If the method of meditation you choose to pursue doesn’t have a built in timing feature (prayer beads, number of cycles of which you keep track) set a timer so you won’t worry about how long you’ve been at it and how long you have left.
As for how long you should meditate, that's going to vary by individual. My advice? Start with what's doable. A short 10 minutes meditation that you actually do is far more beneficial than a 30 minute meditation that you rarely get to. Be consistent and you'll be naturally drawn to let your meditation time expand.
You can have your hands any number of ways: resting on your thighs palms up or palms down, folded together, or in a mudra. Unless your arms are long enough, resting your hands on your knees is not recommended as it will bring your shoulders forward and begin to collapse your chest.
First, in dharana or concentration, we sit down to meditate by focusing the mind on something: the breath, a mantra, or the example I'll use here, a candle flame (signified by the whole candle). There will be distractions: thoughts about people, schedules, pets, bills, breakfast, time, work, and maybe even thinking about the fact that we’re meditating, wondering how it’s going and if we're doing it right. If we stick with it, we let these thoughts go and keep coming back to the object of meditation, the candle flame.
It is through these moments of samadhi, of integrated Oneness, that we gain clear vision. Each stage of samadhi does a little more to burn away our karmic seeds and samskara or habits of thought. Each visit to samadhi allows us to see and reflect unfiltered Reality a little more.
That’s it! That is how we overcome the ego personality and let the Sacred shine through us, and all you have to do is cultivate stillness in your body and mind. Buena suerte, super friends!