Many of the Healing Tao practices require, as a prerequisite, some level of subtle sensitivity and flow. You won't find this point of view in HT books, it's not the party line, but it's so true.
Stretching (especially stretching combined with slow steady deep breathing) is one of the best ways to open up qi flow. If you are just starting qi gong, and you find that your body needs more sensitivity and flow in general, one of the best things that you can do is to take up hatha yoga diligently for at least some months - and then keep some stretching in your regimen as you feel is appropriate.
This point especially applies to the Healing Love practices. Sexual energy is dense and powerful, and it needs supple blockage-free routes in order to flow and transform. One of the best general things that you can do, to facilitate smooth and easy flow of sexual energy through your body, is to stretch consistently.
Stretching, in a Taoist context, is not just about stretching the muscles but is also about opening the channels and one of the primary ways to do this is by activating acupoints. A consistent self-acupressure practice complements stretching to produce dramatically better results.
Supta Baddha Konasana
Supta Baddha Konasana (Reclining Bound Angle Pose) opens up the deep channels of the sexual area (courses the
liver channel which runs through the groin), by
simultaneously opening the pelvis-belly and pelvis-legs angles, in a way that's
most easily achieved with a yoga strap. This is a passive stretch: you lay back and relax into it for a while (5-15 minutes).
Be attentive to breathe all the way through to the lower belly. This is one of the most effective stretches for the sexual area; do yourself a favor and spend the few $'s for a yoga strap.
Also, its accessible. Anyone can do this stretch, by adjusting the amount of back & knee supports (pillows and/or folded blankets work fine), and by adjusting the strap's loop.
TIPS for the adventurous:
Self-acupressure the liver channel prior to stretching.
Sleepin' in Supta
A simple trick is assume the above position (except no pillows and no strap), while napping or falling asleep. This actually goes a long way towards smoothing things.
Combine Supta Baddha Konasana with a mild version of Lin's Sexual Chi Gong Breathing for Men (similar to "scrotal compression" in the HT system). Do not be aggressive with the breathing, as the effectiveness of this stretch is in the relaxing-into-it.
Breathing into the lower dan tien while bridging can be an effective tool for relieving lower heat and stagnation (common difficulties for men, and that goes triple if practicing semen retention). Also, of course, it provides plenty of opportunity for articulating the vertebrae, consciously, slowly. In the kneeling back bend, adjust the angle of the knees in order to extend the back while engaging the stomach; breathe. Shifting position on the exercise-ball emphasizes different sections of the spine.
Vibration Platforms have application re: flexibility.
YouTube video: improving flexibility with vibration.
Obviously, one stretch doesn't work the whole body and, really, the whole body needs to be supple. Below are some resources to explore.
LINKS TO PRODUCTS
Paulie Zink's Taoist Yoga - authentic Taoist yoga
Paul Grilley - Yin Yoga
Sarah Powers - Blending the Insights and Practices of Yoga and Buddhism
Stadion.com - Thomas Kurtz's website. Includes his dvd, Secrets of Stretching (easily worth the $50) and his book, Stretching Scientifically. Kurz takes the approach that leg strength is a necessary complement to stretching in order to get good flexibility (splits), and so he includes a really comprehensive set of leg strengthening exercises, from many different angles, using a variety of modalities. As you can see from Kurz's pictures, his approach results in strength and stability leveraged deeply into the pelvic region. Obvious benefits to jing gong.
Thomas Kurz demonstrating strength and flexibility.
Stretching by Bob Anderson - a long established basic good book
Yoga Journal's Searchable Pose Library
Stretching and Flexibility by Brad Appleton
Thanks! to The Tao Bums (threads 1, 2, 3) for providing reviews and links to the above resources.
As always, getting competent in-person instruction is a good thing.
You might see what's available in your area.