Considerations when dancing in high heels
Your total contact area with the floor is reduced, with most of that contact being located at the front of the foot. For greatest stability, your foot placement should be ball first (as opposed to heel first) - the larger surface maximises friction which makes you less likely to slip.

Your heel clearance from the floor is also much smaller, and the stronger arch support of the shoe tends to distribute forces across the ball and heel more evenly. Both factors affect your ability to time the movement of your leg joints and detect/localise pressure changes through the soles of your feet.

High-heeled shoes constitute an inclined platform, and by wearing them you are effectively moving on a downward slope. Your body usually responds by increasing the curvature of your lower back, tilting your hips forward, and increasing knee flexion. This flexion robs you of a full range of movement at the knee, thereby limiting your control over the lower body action. Reducing the forward tilt of your pelvis by "tucking your tailbone (coccyx) in" helps to compensate for it.
 

Further Practices

1. Merengue Walk
After you've established the habit of picking your spot (on the floor) before placing your foot on it, you can now move the spots forward. Until now, the spots for the right and left feet should be at the same level, a bit more than a hip-width apart. Next try moving the spots forward by a few centimetres of each other before you take each step. This should result in a merengue walk going forwards.

Watch the first half of the clip, where Nathan pedals before walking forward.

Merengue walk - merengue_lower_body_walk_side.avi (4.1 Mb)

If you've got a fertile imagination (like me), you can almost see the spots that Nathan chooses for his foot placement. And if you've let the video play the rest of the way, you'd know that you could use this same practice for a backward walk.

Notes
Take small steps at first, making sure you get the technique right. Increase your step size as your control improves and muscles get stronger.

On the backward walk, make sure your weight is still located to the front part of the foot at the end of the preparation stage. A common fault is for people to let their weight drift to their heels, causing a loss of control. This is particularly crucial if you wear heels. The mark of a good dancer is not in the flashy turns, but in how strong his/her backward step is.
 

2. Varying joint speeds
Assuming that you've developed the control needed for a smooth action, the next thing you can investigate is the effect of increasing the speed of individual joints. What is the effect and what does it emphasise? What kind of music does it go with? Answering these questions helps you understand how you can use your body to generate different types of movement. I'll leave you to explore that avenue on your own.