Set the Date
You don't have to send engraved invitations, but let folks know this is a dinner party, not a just-drop-by-whenever-party or a pot luck. Tell them exactly when to arrive and let them know if they need to bring anything. And no matter how casual, keep etiquette in mind. If you invite your best friend's boyfriend, you have to invite everyone's significant others, so choose your dinner-party draft wisely.
Be Careful of Couples
It's important to invite a good mix of people of different professions and interests, but be careful of their relationship status. Never invite just one or two single people to a party full of couples, and if you do, for God's sake, don't sit them next to one another. (They're there for a party, not blind date flop sweat.) Try to separate pairs of the Partnered Off for the sake of conversation.
Prevent Spats and Drama
It's important to consider the history of your invitees. You may not want to invite your manager and a bitter former coworker, say, or your best friend, and the best-friend-of-the girl-he-cheated-on. And know your crowd -- you might not want to ask your Merlot-loving sailor-mouthed sorrority sister and the ultra-conservative girl from the office.
Make a Shopping List
The week of your party, do as much advance shopping, chopping, pre-portioning and even cooking as possible, so that your day of stress is minimal. Make lists of ingredients, decorations, and to-dos (put the pie in 30 minutes after dinner starts, etc.), and tack it up to the fridge so you can refresh your memory (and not forget to turn the oven on for the roast).
Prep Your Ingredients
Whether you're cooking a massive pot of spaghetti or delicate plates of foie gras, the key to your sanity is pre-prep. You'll be much more sociable if you are just slipping a pan in the oven instead of dicing up vegetables while greeting guests. A few days before, do all your grocery shopping, then borrow a trick from the French and do mise en place -- get everything totally ready until it's good to heat and eat.
Limit the Drinks Menu
Make the drinking part a breeze by serving wine or a pre-made cocktail, or letting guests fix their own libations from a bar area, so you don't have to add mixologist to your hosting duties.
Keep Decor Simple
Keep décor to a minimum. Nice table linens and pretty plates (even plain white ones) say a lot more than a too-tall centerpiece that blocks across-the-table convos. For foolproof flower arranging, pick up bouquets of single-type flowers and display in plain vases along the center of your table.
Set the Mood
Play some tunes, but avoid stuff that's overly loud or attention-commanding as it might discourage conversation. Limit candles to votives and never buy anything scented (Remember the episode of "Top Chef"?) The only odor wafting through your pad should be the delicious dins you're serving.
Buy Big and Buy Backups.
Make sure you have a no-fail appetizer on hand -- like an antipasto tray or roasted nuts -- in case your gougers are a bust. If you're making individual portions of something for dinner -- like filets of meat or fish -- buy one or two extra in case of kitchen disasters. Alcohol wise, a bottle of wine is about five servings, so four bottles are enough for ten guests to have two glasses each, and so on.