In just about every sport, coaches are fond of telling students to "get in an athletic position." It's great advice whether you're fielding grounders, playing guard, returning serve or striking a golf ball, but it's easy to misapply.
A lot of golfers will simply bend their knees and squat down like they're sitting in a chair. Once you're set up like that, your chances of hitting a good shot are virtually nil.
To get in an athletic position for golf, ditch your club for a moment and simply stand tall. Then grab your belt in front with both hands (1). From here, push your belt down into your hip sockets and tilt forward, stopping once you feel the muscles in the tops of your legs engage (2). You should have the sensation that your feet are solidly gripping the ground, so if a 50 mph wind blew through, you wouldn't budge. Now let go of your belt and let your arms hang. This is what perfect posture feels like.
Do this drill a few times, and it will hit home that a good stance truly comes from the hips tilting forward—not from the knees or waist bending. However, if you ever want to confirm your posture on the course, it's easy to quickly sneak this into a pre-shot routine. Just lean your club against your side to free your hands and hold your belt. Then grab the club once you find your athletic position.