DO BE REALISTIC ABOUT THE BUDGET

If you are working within a specific budget, plan the party with all costs in mind. Everyone wants a good deal, but being unrealistic about what your budget can pay for is pointless. At one of Schwartz's restaurants in New York City, the least expensive option would be a cocktail party with a wine and beer open bar and appetizers served family-style.

For up to 50 people, guests could be seated in the back of the restaurant. That means that if you were hosting the party, you wouldn't have to rent out the whole space. For a two-hour party (with no upgrades of food or alcohol), the minimum cost would be about $1,500 before tax and gratuities (though the average client ends up spending about $2,500, she says).

Renting out the entire restaurant with extras such as audio-visual equipment, extravagant flowers, balloons, top premium open bar, passed hors d'oeuvres, customized food and a more extensive array of dishes, or special requests for dishes not on the menu can add considerably to the cost, boosting the tab for a party for 50 people to potentially over $15,000.

DO STICK TO YOUR GUEST COUNT

A good caterer or event planner will always be prepared for an extra few guests. There is a difference, however, between one or two unexpected people and twenty guests whose presence hadn't been anticipated.

Letting the planner know the day before your party that the event has grown by more than ten percent is a big problem. At a time when staff should be setting up the event and adding final touches, they don't need to be searching for additional cases of wine, preparing hundreds more hors d'oeuvres or finding 15 more pounds of salmon.