Thanissaro Bhikkhu

You have to be observant.

When there's sensory contact, can the mind stay continuously undisturbed and at normalcy?

Being observant this way

will enable you to read yourself, to know yourself.

If mindfulness is firmly established, the mind won't waver.

If it's not yet firm, the mind will waver in the form of liking and disliking.

You have to be wary of even the slightest wavering.

Don't let yourself think that the slight wavers are unimportant or else they'll become habitual.

Being uncomplacent.

means that you have to watch out for the details, the little things, the tiny flaws that arise in the mind.

If you can do this, you'll be able to keep your mind protected, better than giving all your attention to the worthless affairs of the outside world.

So really try to be careful.

Don't get entangled in sensory contact.

This is something you have to work at mastering.

If you focus yourself exclusively in the area of the mind like this, you'll be able to contemplate feeling in all its details.

You'll be able to see them clearly

So focus your practice right at feelings of pleasure, pain, and neither pleasure nor pain.

Contemplate how to leave them alone, simply as feelings.

without relishing them.

For if you relish feelings, that's craving.