I did my second Tough Mudder in Austin on Saturday. You'll have fun! Here is my advice:

-If you can, wear something that covers your knees and elbows. I wore Under Armour capris and sweat bands around my elbows. It helped my knees and elbows from getting cut up on all the rocks and whatnot.
-Wear waterproof sunscreen... you'll be out there for awhile
-Hydrate for a couple days before. There are water stations every two miles.
-Bring a towel, change of clothes, a change of shoes, a garbage bag (for your wet, muddy clothes), baby wipes, comb, band-aids, neosporin (just in case),cash and some water. They don't pass out water at the end, so if you want anything to drink or eat, you have to pay at the booths.
-Wear old shoes that you don't really plan on wearing again. Your shoes will get totally thrashed!
-Take a nice, long bath when you get home and pat yourself on the back!

For the Arctic Enema, just hop in and out as fast as you can. If you try to ease yourself in to the freezing water, your muscles will really start to stiffen up. Give yourself a minute or two afterwards to warm up your muscles and get your bearings. The freezing water is disorienting.

The most important part is to have fun! While it's hard, it's a good time! Your fellow Mudders are helpful and make the experience really fun! Good luck this weekend!

I just did the Austin one as well. The arctic enema wasn't anywhere near as bad as I expected. It is a shock and it's hard to take in a breath bc the cold makes you hyperventilate but there are definitely worse obstacles. Definitely put on sunblock. I only put it on my face and now i have an awesome burn on the back of my neck and arms. And very good advice to cover your elbows and knees. I wore pants but my legs are completely bruised up (i tend to bruise anyways) if you can find a way to pad things I would do it. Good luck! I plan on doing another one next year.