Dress comfortably.

There's no reason to dress formally, unless you're taking her to a black tie affair or a very fancy dinner.

If it's an incall for an hour, chances are your clothes won't be on for more than 10 minutes of your whole session, so it really won't matter what you're wearing.

Of course, don't go in looking like a bum.

Have fun!

I often had this same question with the focus on what to wear when she comes to my room. My first few appointments started with me wearing nice clothes like Docker pants and shirt, or a nice pair of jeans and shirt. Then a couple of times since I had taken a shower before she arrived I greeted her at the door in just a towel or robe, maybe wearing underwear at times. With my ATF, there have been a couple of times I answered the door in my birthday suit which she loved. I don't think there is any rule as to what to wear, as long as you are squeaky clean.

I dress for my comfort and the lady's comfort-

Meaning if incall or outcall rather than out to dinner, I wear very clean and neat whatever casual I'd wear to a casual date- I guess business casual describes it best.

If going out to dinner or an occasion first, I dress for the occasion.

and be sure they are clean and in good repair.

You have no idea how much this means to a gal.

Seriously, Show up looking clean and smelling fresh, with a donation envelope at the ready and with a with a pleasant demeanor. Your choice of attire is secondary to your attitude. I would recommend that you dress in a manner that helps you feel comfortable and confident. This is different for everybody.
I've arrived in everything from a Business suit to shorts, sneakers and a full-blown Hawaiian flowered shirt...and everything in between and never been laughed at or turned away. Some ladies may be impressed by a better dressed guy and some may not but if you meet the criteria I mentioned above I seriously doubt that wardrobe is going to effect your appointment.

If you're doing 1-hour appointments that are strictly "private time", there's really no need to get all dressed up.  If you're coming straight from work, you'll be dressed up automatically.  On other occasions, casual (but clean!) street clothes are perfectly fine.  As the joke below proves my point, it's just going to be you and the provider.

Here's a joke on the topic of what to wear (a copy is posted in the Erotic Humor forum as well).
A man who just moved to a new town is sitting in his living room.  Suddenly, there's a knock on his door.  He opens, and there a man he's never seen before standing there.  The stranger introduces himself: "Hi, I'm your neighbor.  There's a party at my place, and I'd like you to come.  There's going to be watching sports, drinking, fighting, and lot of sex."  "Awesome", the new guy replies, "but what should I wear?"  "Doesn't matter", the neighbor says, "it's just going to be you and me."