Start making a stock with cold water. Just cover the bones, meat and/or vegetables with water. Add seasonings but do not add salt. (Salt, if necessary, after cooking.) Bring slowly to a boil over low heat. Using a ladle, skim foam from the top of liquid. If water evaporates, add enough additional water to cover the bones, meat and/or veggies. Skim fat or remove solidified fat after chilling. Strain stock; divide among several containers. Place containers in an ice bath to cool quickly. When chilled, refrigerate or freeze.
For lower fat soups, try these methods. If you're using canned broth that is not fat-free just chill in the refrigerator. After it's cold, remove the top of the can and lift off the solidified fat. Also, when a recipe calls for heavy cream, try using half-and-half or even fat-free half-and-half instead. As long as you don't bring the soup to a high boil, they should work well and your soup will be much lighter.