Veronica is right that you should be putting your weight on the unclipped foot and standing on that pedal. This helps transfer your center of balance down low and means you can get your free foot down to the ground.

Also, a good habit to make is to unclip your LEFT foot. Ever notice that the crown of the road leans to the right? Putting your right foot down means you have to lean downhill -- down the slippery slidy, oily slope!

Road shoes don't have much traction because they aren't built for walking. If you use recessed cleats, this isn't quite so critical but if you use Look pedals (or something similar) you are just asking for trouble!

Last year, I took a beginner friend out to a quiet flat country road and make her take each foot in and out at least 30 times without looking before we rode anywhere near traffic. Seems to have done the trick.