Style File. In addition to browsing fabric centers and furniture stores, you can find great fabrics by looking at catalogs, magazines and manufacturer web sites. Some high-end fabrics are only sold "to the trade" (i.e., design professionals). If you see one you love, contact the manufacturer or your closest design center or showroom to check on availability.
Swatch Watch. Cut swatches to scale based on how they'll be used in the room. The upholstery fabric should be the biggest swatch, followed by the drapes, table coverings, pillows, etc. Layer all of the pieces on a board to see how they relate. Also consider how other materials, from natural stone to stained wood, will round out this setting.
Size Matters. If you select a busy pattern (say, a tropical theme by Tommy Bahama) request the largest possible swatch to make sure you still like it in high doses. At a minimum, be sure the pattern repeats at least once on the swatch.
Your Choice. Major retailers like Crate & Barrel and Storehouse offer a wide variety of fabric choices—far more than you'll see in the catalog or on the sales floor. For an added fee, many retailers will cover your new sofa or chairs with upholstery you purchased elsewhere—this is called "customer's own material (or C.O.M. for short). Note that this will usually add to the turnaround time, which averages about 6 weeks for many manufacturers. If you're in a hurry, ask if the manufacturer or retailer has a "ready-to-ship" line (usually a smaller selection of popular items) for instant gratification.