For a party - make a sangria.... either red or white. Sangrias are fun with your favorite fruit.
For a dinner date... are you cooking? If you are going to a restaurant, then you don't need to worry about choosing the wine now, as you'll see what the dinner specials are and what wines match best accordingly to whatever meals you and your date choose.
If you are cooking at home, then follow Richard's advice below as a general rule of thumb... but pairing wines with food doesn't solely have to be as indicated. There are many meals where you can actually mix or match reds or whites or blush wines - it depends on the meal. If you have meals with thick flavorful sauces, you're going to want something that compliments the meal while still letting the flavor of the meal shine through. If you have a greasier meal, you're going to want something sharper and more acidic and a very dry wine to counter balance the meal's heaviness. If you have a lighter meal like seafood, you will want something crisp, light and maybe even sweeter since it is likely the saltiness of the seafood will need something to compliment it.
If you are looking to have a dessert wine, Muscato or a plum wine is a nice sweet dessert wine. Or you can pair chocolate with Cabernet Sauvignon.