as someone who has meetings with clients fairly often...it's always better to be extra-professional, rather than less.

Get right to the point as quickly as possible, have all necessary materials (paperwork, whatever) ready, so you don't have to hunt for it.

Say what time you think you'll start and end at the beginning, so it doesn't drag on. Feel free to say "I have another appointment at x" or "I have to return a call at x", so that the time limit is there.

Offer water or coffee. I HATEEEEEEE when I go to an appointment, I'm dying of thirst, and no one offers.

Other than that...I hope it goes well ...