There was an ad on tv when I was a kid for Adam's Sour Chewing Gum, whose slogan was "Sour Power!" and "Pucker Power!" Well that should be the slogan for at least part of our step today. We'll be rounding our lips forward into a tight kiss, and then spreading our lips horizontally in a (somewhat psychotic) smile.
Lip rounding is an important part of articulation, and having great control over the action of the lips is vital to the kind of subtlety and control you want in order to do dialects and accents, or character voices that are different from your own, with ease. The muscles we'll be focusing on primarily today are the orbicularis oris muscle, which encircles your mouth, and the buccinator muscle (aka "the bugler's muscle") that spreads the corners of the lips wide, out toward your earlobes.
To do this exercise, you start by rounding your lips forward as if you were going to do a tight kiss, or you were drinking from a tiny cocktail straw. Hold that position for a few seconds, and then relax back to 'neutral'. From here, slowly spread the corners of your lips outward making sure not to turn the corners of you lips upward as you're doing it. The purpose isn't to look happy here, but to spread your lips wide into a very narrow slit. Go as wide as you can and hold that position for a few seconds. Then relax back to neutral.
So now you know the two extremes of the exercise, we slowly speed the action up. Round your lips into a tiny kiss, then spread your lips wide into a psychotic smile, back and forth getting faster and faster and faster.
That's it! The important part is being sure to isolate those two muscles, and trying not to use anything else while you're doing it. Relax your hands, be sure to keep blinking and keep your eyes and forehead relaxed as well!
Next Step: Facial Resonance and Twang