If you get caught in a flash flood,
SEEK HIGHER GROUND IMMEDIATELY!
Always check the local weather forecast for the watershed before going into a slot canyon. Storms that cause flash flooding can occur miles away from a slot canyon, so check the forecast for the surrounding area.
Always let someone know which slot canyon area you will be exploring. Check in at a nearby ranger station or visitor center, and always register for backcountry permits when required.
Always research the slot canyon ahead of time so you are aware of potential trouble spots. Pay close attention to your surroundings during the hike - look for rock ledges, strong tree limbs, and exit points in case you need to make a quick escape. Knowing an escape route ahead of time can save lives.