We have a few guidelines we follow that take into account who's asking (i.e. don't ask the Take-out Queen to make dessert) and what's convenient for us, since we've planned and cooked the meal. Read on for our tips...
Don't rely on guests for appetizers. Whether you are setting out a cheese plate or making something more complicated, you want the appetizer ready to go when people arrive. If the friend bringing the crudite gets stuck in traffic, you're stuck, too. For a guest who barely knows his way around a grocery store, you could ask for an extra box of crackers to have as backup in case you run low.
Booze always works. Of course, most people will happily show up with a bottle of wine. We always appreciate this because we aren't wine experts, and if the guest offering is, we'll happily tell her what we're cooking. But if you are picky about which wines to serve (and probably won't serve the guest's), suggest a bottle of prosecco. It's inexpensive, celebratory, and good to drink pre-dinner. Most people like bubbles.
Salads and side dishes are risky. Potlucks are one thing. If you are planning a cohesive menu, it's dicey asking someone to bring a salad or vegetable unless you know their cooking. You can't be too pushy about what you want, and while we're all for casual entertaining and being flexible, you decided to have the dinner party. You probably know what you want to cook already.
Desserts are safer. Dessert is usually more important to us than the main course, so we like to make our own. But it's easy to ask friends to pick up a good bar of chocolate or some cookies as a little extra. If you aren't as controlling about your sweets as we are, and you have a guest who's offering dessert, take it. Anything sugary is usually decent, and if they forget... see booze, above.
Use their skills. Telling someone, "I've got everything I need. But I'd love your help mixing a few martinis when you get here," especially if that person makes good martinis, lets the guest feel useful and answers the "What can I bring?" question easily.
What's your go-to answer when dinner guests ask what they can bring? What do you like to bring when you're the guest?