My condolence, I'm not joking.

If you're doing activities outdoors: Always bring an extra bottle of water. That is to say, bring a bottle to drink, and then another for when you get thirstier than expected. This season is relatively cool, but you really don't want to be caught unprepared. Also: Arizona has a law requiring businesses to serve water for free if you ask. Don't let anyone bullshit you and ask for money.

Keep an eye on the weather reports, and do not hike down washes, ravines, or narrow canyons if there's a rain storm anywhere nearby. Heavy rainfall several miles away can turn a sunny, dry ravine into a raging torrent that can kill. If you see a road that's currently flowing with water, don't try to cross it, even in a big car. You don't know how deep it really is, and even just a few cms of fast water is enough to sweep a person off their feet and drown them. It doesn't take much more to get a car stuck.

If you're going to Northern Arizona, bring warm clothes. People can be caught unprepared when they leave Phoenix for a day trip and it's 60⁰F, but when they get to Flagstaff 2h later it's snowing.

If you see a Jumping Cholla:

Don't get too close. Their spines are longer than they look because they get so thin as to be nearly invisible.

My condolences.

Mostly joking, I dont know a damn thing about Arizona. There should be some beautiful national parks there but other than that it's pretty empty. Vastly different landscape than the UK though so that should be interesting. Also you're definitely visiting durring the right time of year.

I lived in Tucson for a while. Very good food scene.

Weather is actually pretty nice this time of year.

Nothing really special to be aware of. Stay away from cholla cactus. Lol