You're ready to go clipless (cycling shoes and special pedals) when you want to go farther with the same or less effort then when wearing tennis shoes. I believe they really do make a difference in effort. They also, if properly fitted, will keep your foot in the best position for riding at all times. And, the cycling shoes are stiffer than tennis shoes which will help your feet be more comfortable.

My bike shop put my pedals on my bike and clips on my shoes. They put my bike on a trainer in the shop so I could practice unclipping. The LBS guy adjusted them so they were very easy to unclip. I use the Shimano shoes and clips with more mountain bike-like shoes since I wear them into grocery stores, etc. The road shoes are completely flat and more difficult to walk in while you are off your bike. Either kind should be fine depending on how you will be using them.

I was also told to get use to always using the same foot to unclip at every stop. Make it a habit.

In the two years that I've been using them, I haven't fallen (yet). Nor have I come unclipped on a hill or any other time that I didn't want to come unclipped. And when I have to ride in tennis shoes now, I really don't like it!