Rule number 1: don't be late.
Assuming you have been given the name of the restaurant then determine if they have a dress code. You will want to dress just as you would for a regular interview, with the additional requirement that you meet the standards of the restaurant. It is never wrong to be over-dressed for the restaurant, but very bad to be under-dressed for the restaurant.
The reservation should either be in the name of the partner or the name of the company. That is how you will find them. The staff at the restaurant will escort you to his table. If they are not at the restaurant, wait for them to arrive. If the place doesn't take reservations you will have to call them a few minutes before the agreed time to meet.
I wouldn't call the person before the agreed to time. Treat this as any other interview. If you didn't call them multiple times to confirm the initial interview, then don't call multiple times for this one.
You may want to drive buy the restaurant to find parking or public transportation in advance. This prevents confusion in the critical minutes before the meeting. Also decide what you will order before going to the restaurant. Pick items at the lower prices levels. Take the partners lead on the question of alcohol, but decide what you will order based on the options.