I don't know what kind of clipless you have, I just got the SPD's. I've heard the Looks are harder to pop out of. My LBS made the SPD pedals as loose as possible, and they are easly to pop out of, just turn the ankle and I'm out. A good friend who has been using clipless for years advised me to decide which foot to put on the ground and stick with it -- always put the same foot on the ground. That wasn't hard for me, because even with the old fashioned pedals I found myself putting my left foot down first. So, that is what I've been doing, unclip the left foot as I approach an intersection or something else that could cause me to stop.
The only thing I'd say about doing the one tennis shoe thing is that maybe you shouldn't switch them back and forth, but keep the same foot in a tennis shoe so you'll not get confused about which foot you're using.
Good luck! I haven't fallen yet, but people tell me it isn't as bad as you think it's going to be. (Gulp!)
Louise
~~~~~~~~~~~~~
"You don't really ever have to fall. But kissing the ground is good because you learn you're not going to die if it happens."
-- Jacquie "Alice B. Toeclips" Phelan, former U.S. national champion cyclist