Years ago when I bought a bike with clipless pedals I went to a very quiet street with no traffic and no people and just rode up and down the street. All was well until I decided to start from a stop, was going to slowly, started to tip over and didn't think to unclip in time and I sort of just tipped over and fell. Nothing hurt but my ego though. I wasn't even going. I'd say to stay out of traffic, maybe practice in your yard hanging onto something and slip in/out/in/out for awhile. Then maybe move up to a grassy area and practice. I think if you're trying to do too many things at once (i.e., watch for traffic and road signs, watch for people, clip in/out, etc.) it may be too much at once. Hang in there.