Meditation is practiced in three stages: concentration (dharana), meditation (dhyana), and super-consciousness (samadhi). Concentration is the focusing state of the mind. If you watch your mind, you will see how it is always wandering in so many directions. Most people cannot focus their attention on any subject beyond three or four minutes. In practicing concentration, you develop that ability to focus your mind on one point.
In the second stage, meditation, you maintain the focused state so that the mind holds on to the object of concentration continuously. As you prolong the effortless focus of meditation, there develops an intuitional unfoldment within yourself, and you enter into an experience which you did not have before. This experience, which is unimaginable, indescribable, and beyond all concepts, is termed samadhi or super consciousness.
To further understand the relationship between concentration, meditation and samadhi, consider a simple illustration: Oftentimes children kindle fire with the help of the rays of the sun. First they position a lens in such a way that the rays focus on the point where the flame is to start. Once they have a sharp focus, they keep the lens steady until ignition takes place.
Similarly, your mind normally allows the rays of the Self to be scattered in numerous directions. But through concentration you choose any object and let those rays form a sharp focus. When you can hold that focus, you have entered in to the meditation stage. And if you could maintain the focus for a long enough time, there would be a spontaneous ignition, as it were an experience of samadhi which yields a sense of expansion beyond your imagination. These three stages are implied in every form of meditation, and they must be well understood.
Raja yoga philosophy gives a very precise and scientific study of the development of concentration, meditation and samadhi. An aspirant is asked to first learn to keep his body steady in one pose that is conducive to meditation. Those who cannot maintain an orthodox cross-legged pose is outlined in hatha yoga can sit in a chair or anywhere that is comfortable. What is important is to keep the body as relaxed that you forget about it.
In addition, you have to train your body through proper diet and through health culture in such a way that you are not aware of physical problems. True health is that state in which you do not feel that you have a body. When you are always aware of aches and pains that tell you where your head is or where your hands are--then health is lacking.
Therefore, in its vast perspective, yoga places great emphasis on making the body healthy. But the intention behind this is to render the body fit to maintain one position without any agitation, which is the prerequisite for practicing meditation. If you can hold your body in one pose, then you can begin to work with your mind.
To begin practicing meditation, present before your mind a concrete object that is appealing to the mind and upon which it can focus easily. A concrete object is anything that is visible: a candle flame, a rose flower, a religious symbol, a diagram, the picture of a god or a goddess, a saint, a prophet, or an incarnation.
First look at the form with open eyes, learning to keep your eyes steady for some time. If you wish, the eyes can be allowed to move up and down that form. For example, if you are concentrating on Lord Krishna, you can allow your mind to move up and down His symbolic form and finally choose one spot which you like best: either His face, His flute, or His feet, for example. After gazing steadily, close your eyes and try to mentally visualize that form.
After practicing some form of concrete meditation, move on to abstract meditation. Bring to mind the thought of Divine qualities such as compassion, bliss, purity or peace. Focus on one particular quality, a quality that you want to develop in yourself. If you want to be more compassionate and less angry and harsh, then meditate on the Divine Self as the embodiment of compassion, the embodiment of sweetness. Soon that quality will begin to flow into your personality. Whatever quality of God you meditate on becomes transferred to you. That is a subtle mystical...