My comment isn't meant to conflict with anyone else's here,
just wanted to add in another view: Mostly in the west, when we think about meditation, we think about 'health' effects.
This is because science has been very successful in looking at what
happens to us when some form of it is practiced.
However, health is only a side benefit (what great luck). More traditional
reasons for the practice has to do with inner development (beyond the Waking,
Sleeping & Dreaming states of consciousness). On that basis, one of my favorite,
but simple methods is to:
> Visualize a fish who somehow has been thrown out to the water. It can't breathe,
you see it struggling and naturally, you want to help. Stay with this desire to help. Concentrate for a while on this desire.
The mechanism being triggered here is: your natural sense of compassion. And as the mystical Sufi (as well as many others) tell us, our Higher Self is not in the mind, but in the heart.
A great, but simple little meditation.