1) Make sure you are comfortable. Choose the right shoes. If you're not used to walking in heels, start with a thin two-inch heel, preferably one that you have already broken in. (Later, you can work your way up to walking in higher, less comfortable heels.) If the shoes are new, scratch the soles with scissors so that they will not slip when they touch the floor. Alternatively, you can cover the sole of the shoe with masking tape, if you don't want to scratch your shoes.
2) Learn to stand like a supermodel. Practice your posture, throw your shoulders back, and push your pelvis slightly forward. It might create the illusion that you're leaning back a little, rather than hunching forward.
3) Train yourself to place the ball of the foot down first, and keep all of your weight balanced there rather than on the heel. It may feel strange, but placing the ball of the foot down first gives you more of an elegant stride than a clunky heel-first walk would. It's almost like walking on your tippy-toes, the way ballerinas do.
4) Put one foot in front of the other (literally). Toes should face forward. Your footprints should form a single line, as if you are walking on a rope or a beam. When done quickly, this gives the body that characteristic swing.
5) Make your stride look long and commanding by lifting your legs almost in the same fashion a horse would. For each stride, you want to lift your foot a good distance off the ground (with a bend in the knee) and then place it down a good distance in front of the supporting leg. Don't make your strides too large as this will make you look awkward and ungraceful, but make sure you take large enough steps, rather than just baby steps.
6) Look straight forward, capturing the essence of the clothes you're wearing with the expression on your face. Focus on an object straight ahead of you (but don't stare at a viewer...that is creepy). Keep your chin down a little and your eyes up - you want the spectators to see your face without looking down completly. Keep your head still as your body moves down the runway. Don't swing your upper arms, try to look natural and let your lower arms gently sway as you walk. When you make your turn at the end, take one step back, pivvot on that back foot and let your head be the last part of your body to move.
7) Fingers naturally curl under when relaxed, but don't let them! this makes it look like you have NO fingers, especially in pictures. Just let them hang straight down, shaking your hands out will help your fingers relax and look more natural.
8) Develop your own signature walk. There's no simple formula for walking the runway, and what will ultimately make you stand out is not only how well you can move your body but also how much of your own personality you can inject into your performance to make it memorable. The best way to create your own unique style is to experiment, practice, and get feedback (even if it means taking some constructive criticism).