1. To avoid having only tuna salad (or whatever) to eat, find some way to assign certain types of dishes to groups of guests. It is common to use the first letter of the mundane last name for grouping, as in "A-F brings vegetables, G-M brings bread and baked things, N-R brings dessert, S-Z brings meats. Anyone wishing to deviate from this, please contact the feastocrat." If you hold pot lucks more than once, rotate the letters, you'll get more diversity.
2. Next is to get enough for everyone, but not too much. That is less of a problem in a pot luck, since you can make it the contributers' job to take the leftovers with them. Still, it has proven a good rule of thumb to have people bring enough of their dish for 8 eaters to get a helping of it.
3. Make clear to the guests if there is a kitchen available for cooking, for re-heating only, or not at all. If your guests need the kitchen, be ready to leave it like you'd like to find it at least 2 hours before the feast.
4. Some dishes have to be cooled or kept hot. Is this the responsibility of your guests or yours? Do you have the equipment?
5. I once went to an event where they re-heated the crab soup several times. Everyone who ate off it was sick the following night. If your equipment is lacking, avoid food that gets bad fast. Smoked or salted meat and beef do not get bad easily. Anything done with milk gets bad fast, but is less likely to poison anyone.
6. If you have more than 30 people at your event, the opening of the feast might resemble a bar brawl. Think about a way to get people to the table with the food in small groups. (brass heads first, than ladies, than lords...)
7. Do you have a table large enough to arrange the dishes on?
8. Do you have enough light so people see what's in the bowls and on the plates? (Ever tried to choose from a large pot luck lighted only by 2 candles?)
9. A lot of people have food allergies. Ask the gentles providing the dishes to give you a list of ingredients or put it on the serving bowls. So anyone with allergies can either talk to you to find out what they can eat, or read it on the bowls.

Next, you might want to provide staples, just in case.