I practiced with the bike in a trainer.

Also, while balancing in a doorway is supposed to work.

In a grass field if your tires are wide enough to allow it.

Also, in a parking lot where you can practice while at a higher speed is probably good. Since with speed comes stability on a bike. Just go in a straight line and clip in and out...

Clipless falls happen to everybody.

Were there witnesses? There usually are.