Going to the beach is one person's way of avoiding the present moment by escaping. Reviewing one's to-do list is the mind's way of saying, "Your to-do list is more important than that silly meditation you're doing." And, obsessing over any issue during meditation is another way that the mind exerts control and does its own thing.
So what should be happening during meditation? What should you see? The answer to the first question is concentration on the breath. The answer to the second question is, when we truly concentrate solely on the breath, there is nothing occuring in the mind. Therefore, the moment you lose your concentration, the mind will wander and do its own thing. Meditation has a lot to do with holding your concentration, but first you have to build up your concentration.
Building concentration is a lot like increasing your lung capacity when holding your breath underwater. When you hold your breath underwater for one minute then you're ready to hold your breath for two minutes, then three, then four, and five. Like meditation, it becomes easier the more you practice. And, hopefully you will be able to identify when you're at the beach (in your mind's eye) and when you're really in the present moment.
