This article comes from Woman's Day Magazine and I thought it gave some pretty good advice.
Do spray the inside of the crock with a nonstick cooking spray before every recipe to prevent sticking and to make cleanup easier.
Do cut root vegetables into small cubes no larger than 1-inch squares to ensure they cook in about the same amount of time as the meat.
Do layer root vegetables on the bottom of the slow cooker beneath meat and poultry, as they cook more slowly.
Do fill the insert with solid ingredients first. Place the insert in the base, and then slowly add liquid to avoid splashing and heavy lifting.
Do brown meat on the stovetop before adding it to the slow cooker to add a deeper, richer flavor and color.
Do check food for doneness at the time suggested in the recipe for a minimum amount of cooking.
Do add tender vegetables, pasta, seafood, dairy products and fresh herbs in the last 30 to 60 minutes of cooking.
Do transfer leftovers to refrigerator or freezer storage containers within two hours after they finish cooking.
Do put fresh herb sprigs in a cheesecloth bag, then remove and discard the bag and the cooked, blackened herbs before serving.
Do precook ground meat and sausage to render out the fat before the meat is added to the slow cooker.
Don’t preheat an empty crock before adding food, unless specified in the directions.
Don’t use an extension cord—you’ll risk overturning the pot.
Don’t place frozen foods directly into the slow cooker unless a recipe specifically calls for it, as it throws off the heating of the contents.
Don’t use the slow cooker insert in the microwave or on the stovetop.
Don’t fill the cooker more than three-quarters full, as heated contents will expand, or less than half full, which will cause food to cook too rapidly.
Don’t add strongly flavored vegetables like broccoli until the end of the cooking cycle, so as not to flavor the entire pot.
Don’t stir or turn the food unless a recipe specifies that you do so.
Don’t add seasonings at the beginning of the cooking cycle. The flavor of dried herbs and spices will concentrate and fresh herbs will break down and dissolve.
Don’t wash the hot stoneware with cold water—it could crack the crock.
Don’t use abrasive cleansers or tools that might scratch the slow cooker’s surface.