Tools of Characterization
Actions are a pretty good tip-off that Goneril and Regan are riding the evil train. Actually, that goes for Edmund and Cornwall, too. Goneril purposely fights with Lear; Regan refuses to give Lear shelter; Goneril and Regan lock the door behind Lear when he leaves; Lear's evil daughters ultimately lead troops against him in battle; and Edmund ends up ordering Lear's death.
The whole plucking-out-eyes thing is action in the extreme. Interestingly, it is Albany's lack of action that characterizes him as a not-so-bad guy. He is decidedly not the one to commit these atrocities, yet his passivity holds him somewhat responsible for the crimes anyway.
Regan and Goneril wear "gorgeous" clothes that Lear criticizes. This reinforces the idea that these women are pretty much into their money and power. Cordelia may dress more simply, as she is notably not criticized, which either means she's more modest or her father's favorite, both of which we know to be true.
Shifting gears to our other featured family, we see Edgar spending most of the play naked and smeared in mud. Edgar's lack of clothing marks the height of his suffering not only because he's naked and it's cold, but because the fine clothes he once wore are a reminder of the courtly life that he was driven from.
Sex and Love
Sexual promiscuity and infidelity are both associated with evil in Lear. Check out Goneril and Regan—Goneril cheats on her husband and Regan looks for action only moments after her husband has died. Then there's Edmund, carrying on simultaneous affairs (or potential affairs) with two sisters. Edgar, on the other hand, is essentially asexual, which probably has something to do with his goodness. Even Cordelia's new husband (the King of France) is notably absent from the stage—in this world, good characters don't have sex (or at least we don't hear about their sex lives).
Let's take a look at the hierarchy with Lear's daughters. Goneril, Regan, and Cordelia are ostensibly equal, but Goneril and Regan are older—perhaps much older—and Cordelia is the pampered baby of the family. Some have theorized that this explains Regan's dislike of her little sister: she was the baby until Cordelia came along.
Jumping to our other family, we know that Edgar is the legitimate son of Gloucester and will inherit all of his lands and wealth. In this way he's got a high social position... but doesn't seem to care much about it.
Edmund, of course, as Gloucester's illegitimate son and the product of a casual affair, is defined by this social position and made pretty bitter by it; he is inferior legally, politically, and within his family (remember how Gloucester treats him when they first meet in the play?). Want more? Check out our theme discussion of "Family."
Speech and Dialogue
Edmund is a convincing speaker, whose diplomatic phrases always inch him higher in the world. He spreads poison, but this poison is coated with honey. Edgar, in contrast, starts the play as a character we find to be not particularly coherent. But he gains a bizarre-o eloquence through his mad ramblings as Poor Tom, where he repeats "Poor Tom's a-cold!" in a thin wail and rages about the "foul fiend Flibbertigibbet."
This is a hint that he's changing in other ways as well, perhaps from being privileged but oblivious to a philosophical man of principle. King Lear begins the play speaking in eloquent verse but, in the latter half of the play, he speaks a mixture of prose and poetry, a sign of his descent into Crazytown.