Rinse and drain the lentils in a fine-mesh sieve. Pick through the lentils to pick out any debris. Place the lentils in a medium saucepan. Add water to cover the lentils, plus about 2 inches. You will usually need 2 cups of cooking liquid for every 1 cup of lentils. You can use water, chicken broth, or vegetable broth. Bring to a boil and cook for 20-25 minute, or until the lentils are soft and most of the water has been absorbed.