Sometimes it isn't easy to do, though. When there is so much milk and extra fluid in the breasts, this can put pressure on the milk ducts such that they close down - like standing on a garden hose. Compresses are an effective method of helping that milk to flow. As a general rule, heat gets the milk flowing, and cold reduces swelling. Apply hot compresses to your breasts before nursing, and cold compresses after nursing.
Disposable diapers make wonderful compresses, by the way.
Sometimes, even with hot compresses, there is so much tissue swelling that the milk still won't flow. If this happens, try using a cold compress for 10 minutes or so and then wait 20 minutes or so and try the heat again. A warm shower feels good on a full breast as well. If the areola is so tight that baby can't compress it, try gently hand expressing just enough milk to soften the areola. Your baby will be the most effective pump - once he can latch on correctly.