Buy six different kinds of wine: one sparkling, two whites, two reds, and a dessert wine. For groups of 10 or more, double the number of bottles.
Have two glasses on hand for each guest, one for whites and one for reds. At a formal wine tasting, you'd get a clean glass for each new wine--but who wants to do that many dishes?
Set out a couple of wine buckets or large bowls so your guests can dump any wine they don't consume.
You'll need a good selection of savory snacks (cheeses, crackers, deli meats, olives) and sweets (honey, chocolate, quince paste) to complement the wines. To turn the tasting into more of a meal, ask guests to bring a few appetizers to round things out.
When tasting, always go from lightest to heaviest and from driest to sweetest. This means starting with the sparkling wine before moving on to dry whites (such as pinot grigios and sauvignon blancs) and then to fuller ones (chardonnay, viognier). Pinot noirs or Rhone blends are good lighter-bodied reds; follow with the fuller cabernet, Shiraz, or red zinfandel. Finish up with a moscato, which pairs well with nutty and fruity desserts, or try a ruby port with a piece of chocolate.
Don't fill the wineglasses. If you pour two ounces in each (about a jigger's worth), you'll get 12 servings per bottle.