Putting a lime in a beer is simple: push the wedge into the beer. Consider using a knife to slide the wedge into the bottle for maximum lime flavour.
Photo by Tess Watson.
The problem with the push method is the lime just gets on your hands and the wedge gets stuck in the neck. Over at Bridging the Nerd Gap, they use a knife to channel the lime juice into the bottle. You'll need a steady hand so you don't cut yourself. If you aren't careful, you can do serious damage to yourself -- so only try this trick only if you are comfortable with a knife.
Check out the link for some other tips on using the lime wedge in a beer.
How to properly add lime to a bottle of Mexican beer [Bridging The Nerd Gap]