Study the entire trail you propose to hike. Match its difficulty against the fitness of the weakest hiker. Appoint a trip leader with canyoneering experience.
Adequate water and food amounts vary by temperature and canyon depth, not distance. Eat twice as much as normal. Drink half a quart each summertime canyoneering hour.
Pack 50 feet of strong, light rope. Bring good maps, compass, emergency shelter, flashlight, hat and sunscreen, waterproof clothing and first aid kit.
Errors in judgment in a canyon are cumulative, affected by weather (heat, cold, wind, precipitation, flash floods), elevation, water availability, terrain (boulders, fords, undergrowth, cliffs), survival experience and pack weight.
Slow and steady yields the best progress. Take five minutes off every hour and shed your pack every two hours. Drink continually. Snack often. Take careful note of where you've been, so you will recognize the way back.