OK, concentration, when you know it's not there and you want to work a bit harder to bring it up, OK, raise the mindfulness of the mental noting, get back, get back, get back. That's one way, being a bit more determined. Bring up your Determination Parami, say, "I don't want to indulge in those extra thoughts anymore," be a bit more determined. Reflect wisely. If you see your mind sliding into the same thing all the time, you've got to take a moment, reflect wisely about where it's going wrong, so you can straighten that wrong thought, and then you will let it go quicker. The basic techniques of looking through the body, to see if there's stress, and the change in that. Though all those different techniques can help encourage concentration, if you want to be what we would call a little "macho," the final resort is you grit your teeth, you squeeze your hands, and you bear down on your concentration subject. Sometimes you've just got to put forth a bit more energy.
But in general, when you know there's no concentration, what's the reason for it, what's the hindrance? If you can work towards solving that hindrance, the concentration is going to become more automatic. So keep in mind, you're looking at a teacher who does not stress "Get concentrated! Get concentrated! Get concentrated!" But all the time we're stressing how to lessen the things that are in the way of concentration. It's like there are two opposite sides, but we're working on the deep root of the ignorance. Before we were talking about cutting the chain, and this is the same thing, we're working on the deep root of ignorance. The concentration will automatically come if there's no hindrances. The desire, in particular the desire for concentration, often stops it.