Kent
Google
The falls hike is fun and refreshing on a hot day. Go within a day after a good monsoon rain in the mountains around the falls. Don't wait to long after the rain. The falls and swimming holes diminish quickly.
Bring water sandals/shoes for getting in the water and keep them on. I've picked up broken glass shards in the river/wash bottom, not to mention, aluminum cans, some rusted metal bits, and lots of e-cigs. Visitors aren't great about keeping the area clean.
I keep my phone and car keys (electronic) in a Ziploc freezer bag to keep them dry. Being some water, sunscreen, and a pair of sunglasses, too. Also, if you try to stay out of the water, you'll be hiking near cacti on some steep slopes. Bring tweezers and a comb, or something, for removing cholla balls and spines from your skin. Stick to the water and you won't need that stuff.
When you get to the falls (lower trail), don't dive. The depth is not consistently deep, even after good rains. Have a great swim, though. The pool at the base of the falls can be big. Also, there are some canyoneering opportunities here, if that's your thing.
And for whatever it's worth, know that nudists frequent the area. Don't be shocked. During one visit to the area, a nude man was bothering some other visitors. At other times, nudists have covered up when non-nude visitors came into a particular area. So, like any population, you have all types. Typically, you just find families and groups of young people. And fish, lizards, and snakes.
As for parking, use the newer parking lot or risk receiving a ticket. And no, there are no bathrooms.
The real curse of the area is the hike away from the water back to your vehicle. All that cooling water you enjoyed? You'll be hot and sweating when you reach the parking lot. It's up hill all the way back. Leave near sunset, though, and you won't get fried, plus the sunset view from the parking area is decent.