A good walk will set you apart from everyone on the street. It is easy to train yourself to walk differently and elegantly and sexily.
Start with your hands. Your fingers should not be curled up and not pointed straight out. They should be curved slightly, as if they are pointing to your feet and not your knees.
Work on your arms. The arms must be swinging--nothing is more scary than stationary arms. But you cannot be throwing them all over the place. Watch how much they swing. Allow them to swing just as much as they naturally would want to. For men, swing from the shoulders down and for women, more from the elbows down.
Be cautious of your shoulders. They need to be back. Do not scrunch them up or create unnecessary tension in them, but don't be slouchy. Hold them back and upright.
Take care of the back. Don't be hunched, if anything curve it in slightly, but try to at least keep it is straight as you can at all times. It makes you look slimmer from the side and taller from all around.
Most importantly, the feet. Walk as if you were on a tight rope, keeping one foot right in front of the other. Take the longest stride you can while still keeping it natural looking. By having your steps one in front of the other, you create a sway and a strut that looks natural.