An old adage goes, "As the foundation is laid, so the walls of the house will rise." In yoga, you build a firm and level foundation by focusing on your feet, and from it a strong, spacious, and elegant pose will rise. To create a firm foundation, use the strength of your legs to send strong roots into the earth; make the foundation level by contacting the floor evenly with your feet. Building awareness in the feet in each and every pose may sound tedious—and, yes, it can take years of practice—but it's well worth the effort.
The best way to get to know your feet is to start in Tadasana (Mountain Pose). Try feeling the extreme positions. Make the inner (medial) sides of your feet light, lifting away from the floor, while the outer (lateral) edges stay heavy. This is excessive supination. Next, let the outer edges lift while the inner arches collapse—this is excessive pronation. Ideally, in all of your standing poses you'll balance pronation and supination by keeping your arches lifted while your inner heels and the bases of your big toes stay grounded.