If you want to look good strutting your stuff in heels, it's not so much about your knees and feet as it is about the abs.
For proof, take a few steps in your new heels. With each step, you'll notice your abs tense up and release. So, the single trick to maintain your balance, no mattering how towering your heels, keep your belly to the spine.
Practice the core-driven movement at home, and it won't be long before it becomes second nature. To get the sass right, take small and slow steps. Dainty steps make your walk appear natural. The higher the heels, the smaller the steps. Don't bend your knees, ever! Walk heel-to-toe. Put your heel to the ground first and let your toes follow smoothly. To get your posture right, imagine a piece of invisible string holding your head up. This string is in line with your spine and your chin.