I have four, and they've never let me down:
1. Always invest in good food and drink (make a main course like a salmon or a curry or a big casserole) and if you're going potluck, organize what the majority of people will bring. Some will always show up emptyhanded or bring what they want, regardless, but at least you'll be ahead of the game. If you feed and water people properly, everyone will have a good time. Never wait too long to feed people as they tend to get drunk too quickly and lose interest in food. And ALWAYS provide non-alcoholic drinks/punch for non-drinkers or designated drivers.
2. Have an intimate party –– no more than 8, including hosts, OR a large party of 20 or more guests. Reason: a small party will encourage lots of conversation and "getting to know one another" while a medium-sized party means somebody will always be left out and not everyone will have a comfortable place to sit. A large party means lots of standing, chit chat and general mayhem, and that can be a lot of fun.
3. Do as much as you possibly can before your guests arrive so you will have time to enjoy your own party. You'll still be busy, but not frantic. I set out everything I can think of ahead of time, including glasses, cutlery, plates, napkins, trash, decorations, coat room, candles -- I often fill the bathtubs with water and float tea lights in them. It's a dirt cheap and neat effect.
4. For a large party, invite at least a third more people than you expect to attend. There will always be cancellations and no shows. Never freak out if people don't show up, and never let anybody drive home drunk. I always keep a couple of sleeping bags and air mattresses handy.
Here's some more info from the Food Network.
First:
* Decide what kind of party works for you and your guests: cocktail, buffet, sit down, etc.
* Plan the menu
* Draw up the shopping list
* Take an inventory of pots, pans, dishes, flatware, glasses, napkins, and serving utensils and vessels to make sure you have all the equipment you need for cooking and serving
Quick Tips
* For a quick, easy, and informal party, keep things simple. Purchase snacks like chips, salsa, nuts, cold cuts, bread, crackers, pickles, olives, and prepared salads (potato, coleslaw).
* Before you go shopping or start prepping, clean out your fridge to make room for all those prepared foods and make-ahead dishes.
* They're your friends; feed them right. Incorporate healthier dishes based on fruits, vegetables, and grains.
* If you are feeling a little more ambitious, add a few dishes to the menu above that can be made or assembled a day or two ahead and heated just before serving. Main dishes like casseroles (lasagna, mac 'n cheese, eggplant parmesan), stews, hearty soups, honey ham, smoked brisket (any large meat will do) are perfect. For sides try caponata, marinated salads, a vegetable vinaigrette, or dried bean dishes. And to finish things off, cake, cookies, or pie are all great make-ahead desserts.
* If you are serving buffet-style, then you'll want to plan a little crowd-control. Don’t create a buffet table jam by serving everything on one big platter. The proceedings will run smoother if you spread things out on smaller platters with the sides and meat pre-sliced.
* There's no need to foot the bill for the wine as well as the food. Make it a BYOB and ask your guests to bring wine, beer or soda. And ask them to bring a particular type of wine or beer to go along with the food you're serving, if you like.
* Make well placed and clearly marked areas for trash.
* Have plenty of ice made.
* Set and dress your table before your guests arrive.
* If serving a buffet, make small cards to identify the dishes.
* Be creative: use your water glasses for crudités, breadsticks, and even flowers.
* For easy access and a prettier presentation, have all related condiments in small bowls with spoons, all in one area.
* Wrap utensils (either plastic or silver) in napkins and place them in a basket for your guests to easily grab and hold.
* Keep plastic bags and containers handy to pack leftovers for your guests and yourself.
Portion Control
* Count on 3 drinks per guest.
* Provide guests with non-alcoholic drink choices.
* Assume some of your guests will be vegetarians.
* Count on 4 to 6 hors d'oeuvres per person if you're serving a meal. If you're just serving hors d'oeuvres with cocktails, the amount goes up to 12 pieces per person.
* A portion of meat per person is 1/4 to 1/3 pound.
* A portion of vegetables, rice, pasta, or salad is 1/2 cup.
* A 9-inch pie or tart (after a large meal) will serve 8 to 10.
* Always prepare a selection of items that can be served at room temperature. That way you don't have to worry that your hot entree will be getting cold, or your cold dessert will be melting.