When I started with Clipless, first thing I did was to clip/unclip against the wall 10 times (until I knew exactly how to unclip). Then I went to the grass and rode in circles for 5 minutes stopping and unclipping as many times as possible. Then I went to the real life....
Suggestions:
1. Always unclip both pedals at the same time. If you unclip just one, you might fall to the clipped side.
2. Keep in mind that you won't fall while pedaling, it always happens when you stop.
3. Keep in mind that you will fall at least once. It is part of learning process.