First of all, congratulations!
You will do fine.
When you get to the restaurant, the first thing you do after you sit down, is place your napkin in your lap.
If it's a more formal restaurant, and there are two forks on the left side, then you use the smaller (or the one furthest from your plate) for the salad or appetizer. Then, you use the fork closest to your plate for the main entree.
Don't order the most expensive or the least expensive thing on the menu.
Don't order an alcoholic drink.
Follow your hosts lead to see if he/she is ordering an appetizer and an entree.
If for some reson you need to get up from the table during the lunch, excuse yourself and place your napkin on your chair.
After you are done eating, you place your napkin to the left of your plate. Don't refold it, but don't ball it up either. Make it into a sort of long tube.
While you are eating, but not finished with the meal, there is a way to put your silverware.
Here is a website that will cover a lot of this stuff.
http://www.professionalimagedress.com/dining-etiquette-seminars-eating-styles.htm
Most importantly, say thank you at the end, and follow up with an email expressing how nice it was to meet them and to thank them for lunch. Say that you appreciate that they took the time to meet with you, and that you hope that you will the chance to work together in the future.
Also, remember that they have no idea that you aren't a seasoned restaurant diner, so they probably won't be scrutinizing your dining habits.