Qigong breathing practice begins with a simple method called Following the Breath. This practice introduces you to internal awareness and training of the mind to stay focused in a relaxed manner. Once you have practiced this for a couple of months, you can advance to abdominal breathing.
When you first start abdominal breathing, you may not notice any movement in your dantien area. If that is the case, keep visualizing a ball of energy in the center of your body in your lower dantien. Visualize the ball massaging the sides of your lower torso and lower back as you are inhaling and exhaling. Over time the perineum area will also expand and contract. Don't use force, instead, allow the breathing to open up areas that are tight or without feeling. Over time, perhaps a period of several weeks or a couple of months, the energy ball in the dantien will grow and will open up your lower back and the sides of the abdomen and you will feel the physical sensation of expansion as well as the energy.
You may also encounter blockages on the way down to the dantien. Let the breath do the work, just following it as it goes in and out. Let go and release tension and energy blockages on the exhalation, Doing without doing will facilitate your advancement in your practice. For a detailed manual on advanced practices in qigong breathing, read the book by Yang Jwing-Ming on Embryonic Breathing.
Another resource for beginners to consider is a guided meditation CD by Bruce Frantzis, a Taoist Lineage Master. This meditation, called the TAO of Letting Go: Meditation for Modern Living. Frantzis guides listeners in meditations that allow feeling contractions and other types of blockages within the body. As the CD progresses, he also teaches the methods to dissolve physical as well as emotional blockages that are encountered. Frantzis also has published another CD called Taoist Breathing for Tai Chi and Meditation: Twenty-Four Exercises to Reduce Stress, Build Mental Stamina, and Improve Your Health, which has 24 qigong breathing exercises for increasing internal awareness.