Kashalha, as vipassana is a too broad a word encompassing many aspects of Dhamma, I would recommend this one meditation, that can be done when you are walking, sitting, lying, or any other posture that when sleeping. It is called Sati Sampajañña. Alertness and awareness come under the Pali word, sampajañña. Sati means keeping something in mind, like remembering to stay with the breath, remembering the various things that help in the training of the mind. Our happiness, our lack of happiness, depends on our actions. So that’s where we focus our attention. That’s what we should keep in mind. This is called dhammanussati, keeping the Dhamma in mind. This is why the Buddha has us listen to the Dhamma, read the Dhamma. Whatever thinking that you do, it needs to be through the Dhamma.
When you create a frame of reference here in the present moment, there are lots of things you can tune in to. You can choose the body in and of itself. You can choose feelings, mental states, mental qualities in and of themselves. Those frequencies are on the path. Other frequencies are off the path—there is such a thing as Wrong Mindfulness, you know. Our meditation consists of choosing the frequencies most beneficial for the mind.
Whenever your thoughts go to recollecting your past incarnations, try to get them out of your mind, as they are a-Dhamma. To be consciously forgetful in that way requires an act of mindfulness—in other words, deciding which level you’re going to tune in to while you let everything else go for the time being. Of all the sensory input that comes in at any one particular moment, you make a choice of what you’re going to pay attention to, what memories, what frame of reference you’re going to bring to that particular moment. And it’s an important mental skill to be able to shift your frame of reference as necessary.
Being mindful means being very deliberate and clear about what you bring to whatever you’re doing: what you’re going to remember, what you’re not going to remember, what you’re going to recollect, what you’re going to let go, which things are useful to recollect right now. If you wanted to, you could sit here and spend the whole hour thinking about facts that would make you totally miserable, but what does that accomplish? We’re sitting here to think about things that are useful for the mind, so remember the things that are useful for the mind, that will help it develop. As for the other voices coming in and out of the mind, listen to the ones that are helpful and ignore the ones that are not. You can be selective.
This way, mindfulness becomes a quality we can apply to everything we do. And instead of making us unable to function, it actually heightens our ability to function, because we understand the process that the mind goes through.