Catch 'em all without leaving home
Warning: this can get you banned.
While GPS spoofing defeats the intended real-world exploration of augmented reality, using a jailbroken iPhone will let you mess with your location services. As detailed in this video, you the LocationFaker app lets you move your GPS location without actually going to that place.
This means you can get to that gym down the street -- or that spot with the Mewtwo on the other side of the world -- all from the comfort of your couch. You'll only burn as many calories as one does while moving a pin around on a smartphone, which is to say, not many.
Additionally, this can help you accrue mileage for incubating eggs.
Use lures and incense to attract Pokémon
This is pretty basic, but you can activate incense to attract Pokémon to you personally. If you're not into wearing Pokécologne, though, you can just loiter about a PokéStop with a lure on it. Chances are, if it's in a happening part of town, you can just be a Pokéfreeloader.