It's important to monitor all dogs that are wearing coats or sweaters carefully for signs of overheating; dogs already have a layer of fur, and many healthy, medium-sized dogs will be just fine in weather that isn't too cold. While your pup is all jacketed up, check for excessive panting or scratching at the piece of clothing -- that's an indication that your dog isn't too thrilled with his or her new duds. You want to avoid discomfort, so be careful while shopping for that jacket or sweater.
When selecting doggie outerwear, it's important to look for apparel that covers the neck and belly, leaving the legs free to move (unless your dog is particularly sensitive to the cold, and needs leg coverage as well). As for material, it's best to try different kinds and see what your dog likes best. A good blend of washable wool and cotton or acrylic is a good bet to avoid itching, according to PetMD. It's a good idea to make sure the jacket is waterproof, too, especially if you live in a rainy or snowy spot. If your dog is prone to chewing or swallowing small objects, look for a coat without zippers or ties that could fall off and be gobbled up.