The Anapanasati sutta is probably the most detailed set of meditation instructions in the Pali Canon. At its core, it is a set of 16 meditation activities, fourteen of which 'one trains oneself' to do. These 14 activities divide up into four 'foundations of mindfulness', or in Thanissaro Bhikkhu's phrase 'four frames of reference'.

To start with, the meditator is just aware of the breath in the present moment:

The concept of 'evaluation' is Thanissaro Bhikkhu's translation of the Pali word vicara, and is an integral part of the Buddha's prescription for the meditation he advocates, at least for the first stage of it (the first jhana - note that I use the word jhana here as in the Pali Canon, not the high-octane wham-bam jhana of the Commentaries):

The meditator enters and remains in the first jhana: joy and pleasure born from centeredness, accompanied by directed thought and evaluation. He permeates and pervades, suffuses and fills this very body with the joy and pleasure born from centeredness, so that nothing of his entire body is unpervaded by them.

It is often said that you must not think in meditation - I write about this attitude elsewhere on this site. Here I want to point out that the Buddha clearly says that at least in the first stage of meditation it is healthy to think. And he suggests two modes of thought: vitakka, which can be translated as 'directed thought' or 'reflection'; and vicara which is like 'evaluation'. It seems to me that what the Buddha meant by 'evaluating' your experience as you have it is very similar to Focusing. When I first understood how the concept of Focusing can apply to my meditation process, I immediately thought 'this is surely what the Buddha meant by vicara'.

Anyway, back to the ideas of the Anapanasati Sutta: For true insight, I need a steady and clear mind. So the primary aim in my meditation is first to bring this about, using the breath as it is and as it affects my body. The idea is not to control the breath too much, but to take natural breaths in such a way that is comfortable, so that the mind is happy to stay there.

I find I need to experiment to get comfortable (evaluation, Focusing); often what I think of as 'natural breath' is in fact a set way of breathing, and by changing it a bit I get to a more 'natural breath'. Two particularly fruitful ways of experimenting with the breath to get it comfortable and natural are:

(1) to imagine the air entering the body in other ways than through the nose/mouth and throat - for instance, through the pelvic floor, or in and out through the whole torso, like a sponge;

(2) to accentuate the out-breath, either by forcing the air out more than usual (using the intercostal, or rib, muscles), sucking the stomach back in, or simply holding the breath after expiration a little more than normal. This then encourages the in-breath to be fuller, and often feeling more natural.

Having the mind at ease, riding on the breath, is both restful and enjoyable. It is both immensely satisfactory as it is, and if there is somewhere to go in meditation (like the jhanas) then this is the way to get there.

However, as anyone who has practised any type of meditation for five minutes knows, things are never this smooth. The mind jumps around, thinks extraneous thoughts, makes you drowsy - in short, for some meditation sittings you are lucky if you can focus on one breath out of a hundred.

So what do you do? Ajahn Lee (a Thai Buddhist teacher in the Forest Tradition) gave this analogy: You are like a hunter-gatherer of old, whose true home is around the fire with your family. But, in order to maintain this, you need to go away from the hearth and the home from time to time to forage. Foraging is not what you want to do, but it is necessary to do it in order to maintain the home.

In a like manner, at ease riding on the breath is our 'home', where we want to be in meditation; but this is not always possible, and so we need to go foraging. There are many ways of 'foraging', but the essence is to deal with the distraction in as skillful manner as possible, and learn from it in so doing. As Jason Siff says, there is nothing thrown up by the mind that cannot be used as a learning experience to further our meditation skills. Here are a few examples of foraging:

So I am focusing on my breath - a thought or sensation comes to distract me - I deal with it with the primary aim of having a focused mind at ease in the breath. That means initially can I just ignore it? If so, I do so. If not, I let myself be aware of it, in an open, even welcoming way. Perhaps I examine what the pain or thought is, just being aware of it without agenda, and what is around it, in no particular hurry - I am quite happy to let the rest of the meditation sitting be taken up with this thought or sensation; I can go back to the breath in my next sitting.

I may see what effect the emotion or thought is having on my body. Emotions can be very body-centered. Think of our language - when we are nervous, we have butterflies in the stomach; when we are sad we have a lump in the throat; and so on. Bringing my emotion or thought into my body can be interesting and educational.

If the strength of the distraction or pain is great, I may need to go 'nose to nose with it' (John Kabat-Zinn's phrase), really focus on it, immerse myself in the raw sensations. Very often, what seems initially like a solid wall of pain will break up into shimmering patterns of energy if I focus on it and sink into it, as it were; the solidity vanishes.

If there is too much going on to allow focus on the breath at all, then I may need to do something 'completely different', as Monty Python would say. Being aware of my body, other than the breath, is a good place to start; either with a whole sense of body (the body as it is, in and of itself, as the Pali Canon Suttas say), or else systematically focusing on parts of it, in some kind of order. Thanissaro suggests a 'bones scan' where you become aware of each bone of your body in a prearranged sequence; or Goenka teaches a systematic body scan, where your attention moves through the body in cross-sections, rather like a real medical scan. I write about how I do this elsewhere on this site. After ignoring the breath for a while, and focusing on something else, sometimes when I go back to it I become much more at home with it.

Or I may 'forage' by becoming aware of my surroundings - the body in space, listening to the sounds around me brings me a sense of space in which I exist, both physical and mental. Buddhists often speak of 'spacious mind', in which all my usual distractions and mental clingings still exist, but are contained in a 'spacious' consciousness that has room for much else, so that they do not crowd me out and take up too much of my energy.