Whatever you do, avoid embedding exposition by having one character say to another, “As you know …” This is commonly given in science fiction stories by a “Stapledon”, which is a character who gives us an info dump, usually one at great length and without interruption (The term is ignominiously pays homage to science fiction writer Olaf Stapledon, who regularly made use of this technique.). It’s an obvious info dump and immediately flags to the reader that the forward movement of plot is about to be slowed, that he is about to be lectured and the viewpoint may be violated. As award-winning science fiction editor Gardner Dozois said of the Stapledon, “That’s probably the most common beginner’s mistake …”