Watch the Holding the Guitar online guitar lesson by Rich Maloof from Acoustic Guitar For Beginners

If you start out holding the guitar comfortably, the only pain you should ever experience is on your left-hand fingertips - and even that will go away after the first few days of practicing. Mind these tips on posture to play in comfort.
You'll also want to make sure your guitar is in good working condition. Even the finest guitars go out of whack. Since wood is an organic material, it's vulnerable to changes in temperature and humidity. Any guitar that is new or has been sitting around unused for a long time will benefit from a quick tune-up and restringing at your local music store.