To pick up on something David. 'Give it your all as far as attempting to concentrate while meditating...'
It may be just a figure of speech you used, but if it's what you are actually doing it sounds like you may be trying to 'do' meditation.
Which isn't possible. You can't manufacture the meditative space, it's always been there, it just 'is'. (in ACIM terms it's when we start to to open, when we probably intermittently open to 'hearing' the Holy Spirit via our intuition or other means over the chatter of the thinking mind) The intention is to become aware of it, to develop the ability to rest in it (language doesn't express this very well) but the problem is that the moment you 'try' to do it, the more you intensify the thinking mind, the more you thicken the fog of thought and the more obscured it becomes.
Trying to 'stop' thinking has the same effect, never mind that it's a contradiction. While meditating you don't try to manipulate your thoughts, you instead seek to rest easy and watch the thoughts arise and decay.
If as happens we find ourselves getting sucked into a line of thought (what's for lunch!!
or whatever) it make take us with it for some time before we recognise what has happened. When we do recognise we've been taken in just quietly drop it. Don't beat up on yourself, and don't allow yourself to get angry or frustrated - just say to yourself 'not just now thank you', and go back to watching your thoughts.
Meditation (contrary to popular perception) is not about 'making' your mind lie quiet. It's about practicing the ability to rest quietly and with equanimity while thoughts come and go on the screen of your conscious mind - without getting sucked into identifying with them.
Another way of putting it is perhaps that with time and practice there's a part of mind that develops the ability to stand aside and just quietly observe what goes on in the thinking mind while its led astray by the 'mad monkey' of ego.
With time and lots of practice a quieter mind may emerge - but it takes many many years for some to reach a quieter mind, and 'achieving' a quiet mind is not the sign of meditating well. Staying quietly with the task, not getting discouraged, and eventually becoming so that this equanimity is undisturbed no matter what arises in the mind (and eventually in our external experience) is what its about.
Pema Chodron (a well know Buddhist nun and teacher) famously writes broadly to the effect that she's not by the criteria of 'quiet mind' had a single decent meditation to this day. (and that's after an adult lifetime of meditation) The point though is that this is not a problem.
Over time (but it may take years) the mind may tend to quieten, but as soon as we try to actively force it, or become upset or frustrated we go backwards.
There a very old training in the nature of this process that's usually expressed in pictures like the one here from a Tibetan Buddhist monastery:
http://www.reep.org/gardens/buddhism/images/1religion/tamingthemind2_l.jpg The page (which nicely explains some of the why of meditation in the Mahayana Buddhist view
http://images.google.ie/imgres?imgurl=http://www.reep.org/gardens/buddhism/image... - its essentially the creation of the space needed for wisdom and compassion to arise. The generation of esoteric experience is not the point...) explains the picture as follows:
'Painting from a Tibetan Buddhist monastery:
This painting from a Tibetan Buddhist monastery is like a cartoon strip showing stages of a monk calming his mind through meditation training.
* At the bottom you see a new monk whose mind wanders so much in its own directions that it resembles a muddy elephant led by a naughty monkey. The monk is running after it.
* Half-way up, his mind, the elephant, has been partly cleaned up and it is the monk who is now leading it – though the monkey is still interfering by pulling the elephant’s tail from behind.
* Further up, the elephant is now clean and the monk alone is in charge – he is saying goodbye to the monkey.
* Next the monk can get the elephant to lie down and finally he can ride it.
* At the top the monk is fully in charge of the elephant, his mind, and is now riding down to put its powers to good (wise and compassionate) use.'
Try not either to get attached to or to strive after esoteric experience of one sort or another. It's part of the total experience that may (or may not) arise, it can be a nice confirmation that our mind training is progressing, and it can play a role in our development by presenting learning opportunities and deepening our knowing, but it's essentially a side show which becomes a diversionary cul de sac if it becomes an object of attachment in itself.
A practiced meditator eventually develops the ability to drop into these states very quickly and easily, but it is a matter of mind training. Hemi Sync can help a lot too.
PS (a later add-on) Two basic types of meditation are taught at first - 'shamatha' (calm abiding) and 'vipassana' (insight meditation)
Development of a reasonable capability in the first is generally seen as desirable before starting the second - in that if it is attempted (insight meditation on a given topic) before there is some stabilisation of our mind the result tends to be out of control and often obsessive thought which drowns out any intuitive insight we might otherwise have been able to access.
On the other hand most find that as space and stability start to develop in the mind that insight naturally arises - both when meditating, and in normal life, whether working a topic or not. (my own experience is that it works best when not trying, as i often get too intense if i try to do it). Insight is not anyway the result of 'thinking' about a topic. It's more about resting with the topic lightly in mind and passively awaiting what arises. (its essentially the creative process - and explains why our creativity dries up when we get uptight) Depending on your tradition the source of this insight can be spoken off as being the prompting of the Holy Spirit, of higher mind, of our true nature and so on.
The other sure fire indicator that space and stability are starting to arise is often an indeterminate but very lovely feeling of being comfortable and easy with one self - things, people and situations that used to bother us no longer do, and in the resulting space we find ourselves very often feeling or spontaneously expressing compassion, and doing the wise thing in situations - which often is just to let things 'be' instead of panicking, and rushing in with inappropriate actions.
One of the side effects is often the emergence of a deep trust or faith in 'flow' - the knowing that life is basically benevolent, and that if we can rest easy act wisely that it tends to being to us exactly what we need at right time on our journey.
None of this can be forced though. Do work and hopefully it emerges, wells up from somewhere in the depths of mind. We're talking reducing the intensity of/allowing the obscuring fog of thought to clear so that we can access these attributes and feelings. Eventually they emerge and are just 'there' - it's a process not of acting directly to make something happen, but of 'becoming' something else. Nothing whatsoever to do with the outcome of an intellectual or conscious thought process.
The creative power, compassion and wisdom of this sort of knowing can deliver a truly amazing transformation of the individual concerned.
Pardon the length, but maybe it may help some others too. What i've tried to set out is a very typical Tibetan Buddhist expression of teaching on meditation.