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As with any celebrated viticultural region, Sonoma has become a place of pilgrimage for people who love wine, and while visitors simply set out by car visiting tasting rooms more or less at random, a little advance planning can make your Sonoma Valley sojourn a more targeted and educational experience. Even if you don't consider yourself much of an oenophile, consider reading up on the region's wines ahead of time, and develop a short list of top wineries you most want to include on your wine-tasting itinerary.

One good approach is to concentrate on wineries that are known for excellence with a particular grape variety, such as Zinfandel or Sauvignon Blanc. By comparing wines made from the same grape variety, you can cultivate a sense of how that grape can achieve different expressions in the hands of different winemakers.

Another option is to focus on a particular sub-region or climate zone within the Sonoma Valley appellation. The Carneros district, for example, which straddles the southern reaches of Napa and Sonoma, has a relatively cool climate that is ideal for growing Pinot Noir and Chardonnay grapes, both of which are used in the production of fine Champagne-style sparkling wines. Warmer conditions farther north in the Sonoma Valley are better suited to Cabernet Sauvignon and Merlot. Bear in mind, however, that the location of a winery doesn't necessarily reflect the origin of the grapes, as many winemakers acquire grapes from vintners throughout Northern California.

Finally, don't make the mistake of limiting your tasting to free samples. Many of the better Sonoma wineries have begun to levy a small fee for anyone who wants to taste, while others offer some samples for free, but charge visitors for tastes of high-end reserve bottlings and older "library" wines. If you're at all interested in fine wine, these premium flights can be well worth the extra cost, and in many cases the tasting fee will be subtracted from the cost of any wine you purchase at the winery.

Lists of local wineries, with links to their individual Web sites, are available online at www.sonomavalley.com and www.sonomavalleywine.com.