Wearing the wrong shoes when hiking in
Yes, those retro Jordans you got are indeed “mad tight, yo.” But they’re also mad uncomfortable and mad dysfunctional if you try and wear them to hike through the desert. If you’re planning a trip that involves more than just a glimpse from the observation deck, buy a pair of hiking boots with good traction and ankle support. You don’t need to go blow half your paycheck at REI, but consider the shoes a cost of the trip. Then break them in for a few weeks so you’re not fighting blisters during your hike.
Forgetting the hike out is a LOT harder than the hike in
You’re probably familiar with the laws of physics, and that fighting gravity is more physically exerting than going with it. But you may not understand exactly HOW much more exerting until you’ve been walking up a rock cliff in 110-degree heat for an hour and haven’t even gotten a quarter of the way back. Remember, you're doing the reverse of climbing a mountain. Hiking down it first, then up! So think of your hike into the canyon as a warmup; the real work starts when you get to the bottom. Just be sure to ration your food, water, and time accordingly. And speaking of time, depending on how far you intend to go, it's a good idea to leave BEFORE 7am. The temps are cooler, and you leave yourself more time to hike out assuming fatigue sets in.