General Rexing Tips
Put an elastic hairband on each wrist. If you need to use your hands inside your rex, you can pull the arm in, twist the hairband around the open end, and your suit will stay inflated. Sometimes I just keep the rex arms ties with bands and pushed out so they're visible and just keep my human arms on the inside so I can check my phone or take a drink or just be comfortable. People WILL try and hand things to or shake or high five your rex arms though, even if you're not in them.
Invert that zipper!
If your suit doesn't have a double-sided zipper, when you're zipping yourself in, grab the zipper pull and tuck it inside at the top. That'll make it easier to unzip yourself later.
I suggest getting a large rechargeable power bank with 3 USB-A slots (and maybe a USB-C). That way, you can run both fans at the same time you have your personal neck fan plugged in or recharge your phone.
Don't want the rexxing to stop? It's a good idea to carry spare batteries and a spare fan or two.
You will probably want to lean forward and duck to go through most doorways. It is also helpful to lean forward and hold the railing when going down escalators. This will lift your tail and keep it away from the collapsing step seams.
Feel with your feet!
You're going to have a hard time seeing your legs. If you know there's a curb or step up coming, keep your feet low to the ground and feel forward until you touch the step with your toes. Now you know where to step. Similarly, if you need to go down stairs, step down with a foot, but before putting weight on it slide your foot back until your heel makes contact with the vertical edge of the step above it. That will help you avoid misplacing your next step and falling.
Subtle movements don't come across well outside the suit. If you want to entertain others, make big exaggerated movements. Jumping or bobbing up and down will also bob the head. Running forward will usually throw your head back (especially if you only have one fan). You can also bring an arm inside the suit and treat the rex head like a puppet, pressing down on the top jaw to close the mouth, or pushing to the side to turn the head slightly.
The more you move, the faster you will push air outside of the suit and the more you'll deflate. This is especially noticeable in suits with only one fan. Give yourself a still moment to re-inflate if you notice things getting saggy.
Adjust the height!
Window up higher than you'd like it? Scrunch the legs of the suit down further on your legs. The suit's "crotch" may be mid-thigh on your or even closer to your knees. That will lower the height of the window.
Window down lower than you'd like? Pull up your rex pants! Really, just scootch the legs up higher on your legs and the suit's "crotch" is more like you'd wear your pants. Your ankles may show out the bottom, but that's okay, this isn't the 1890s!
Bring a friend!
Having a friend (or "handler") with you who's not wearing a suit can be useful. They can help you navigate areas, open doors, communicate clearly (it's hard to hear inside the suit, and hard for people to hear us), run interference if people start treating you like a prop instead of a person, and keep an eye on your hydration and heat levels.