Listen to everything that is said, and see everything that is done. Observe the looks and countenances of those who speak, which is often a surer way… - Philip Dormer Stanhope

Common sense (which, in truth, is very uncommon) is the best sense I know of: abide by it; it will counsel you best.

Remember, then, as long as you live, that nothing but strict truth can carry you through the world, with either your conscience or your honor unwounded. It is not only your duty, but your interest; as proof of which you may always observe, that the greatest fools are the greatest liars. For my own part, I judge of every man's truth by his degree of understanding.
Remember that I shall see you in the summer; shall examine you most narrowly; and will never forget nor forgive those faults, which it has been in your own power to prevent or cure;

Gratitude is a burden upon our imperfect nature, and we are but too willing to ease ourselves of it, or at least to lighten it as much as we can.