"About meditation..."
by ven. Ajahn Chah

When sitting in meditation we are told to close the eyes, not to look at anything else, because now we are going to look directly at the mind. When we close our eyes, our attention comes inwards. We establish out attention on the breath, centre our feelings there, put our mindfulness there.
Let the breath go naturally, don't force it to be short or long or whatever, just sit and watch it going in and out. When the mind lets go of all external impressions, the sound of cars and such will not disturb you. Nothing, whether sights or sounds, will disturb you, because the mind doesn't receive them. Your attentions has gathered on the breath.
If the mind is confused and won't concentrate on the breath, take a full, deep breath, as deep as you can, and then let it out till there is none left. Do this three times and then re-establish your attention. The mind will become calm.
It's natural for the mind to be calm for a while, and then restlessness and confusion may arise again. When this happens, concentrate, breath deeply again, and then re-establish your attention on the breath. Just keep going like this. When this has happened many times you will become adept at it and the mind will let go of all external manifestations. External impressions will not reach the mind. Sati (mindfulness) will be firmly established. As the mind becomes more refined, so does the breath. Feelings will become finer and finer, the body and mind will be light. Our attention is solely on the inner, we see the in-breaths and out-breaths clearly, we see all impressions clearly. This is called Samadhi.
After watching the breath for a long time, it may become very refined; the awareness of the breath will gradually cease, leaving only bare awareness. The breath may become so refined it disappears! Perhaps we are "just sitting", as if there is no breath at all. Actually there is breathing, but it seems as if there is none. This is because the mind has reached its most refined state, there is just bare awareness. It has gone beyond the breath. The knowledge that the breath has disappeared becomes established. What will we take as our object of meditation now? We take just this knowledge, that is, the awareness that there is no breath.
Unexpected things may happen at this time; some people experience them, some don't. If they do arise, we should be firm and have strong mindfulness. Some people see that the breath has disappeared and they get a freight, they are afraid they might die. Here we should know the situation just as it is. We simply notice that there's no breath and take that as our object of awareness. This, we can say, is the firmest, surest type of Samadhi. There is only one firm, unmoving state of mind. Perhaps the body will become so light it's as if there is no body at all. We feel like we're sitting in empty space, all seems empty. Although this may seem very unusual, you should understand that there is nothing to worry about. Firmly establish your mind like this.
When the mind is firmly unified, having no sense impressions to disturb it, one can remain in that state for any length of time. There will be no painful feelings to disturb us. When Samadhi has reached this level, we can leave it when we choose, but if we come out of this Samadhi we do so comfortably, not because we've become bored with it or tired. We come out because we've had enough for now, we feel at ease, we have no problems at all.
If we can develop this type of Samadhi, then if we sit, say, thirty minutes or an hour, the mind will be cool and calm for many days. When the mind is cool and calm like this, it is clean. Whatever we experience, the mind will take up and investigate with wisdom. This is the fruit of Samadhi.