According to an article in Natural Awakenings, "Many of us suffer with chronically cold hands and feet and can’t seem to get or stay warm. Heavy layers of clothing and drinking warm liquids such as coffee, cocoa and tea cannot combat the feeling of “chilled to the bone.” Bringing heat to the body can be accomplished by practicing breathing techniques, such as the qigong Tumo practice.
First, visualize that you are breathing in through the top of your head and imagine that you have a very long and narrow neck, and a full, round base. Your breath travels down through the neck of this “bottle.” When it becomes full at the bottom, imagine corking it to keep the breath from escaping for as long as possible. As you come to the end of your endurance, release the breath very slowly. At the same time, imagine that the qi is like a mist that separates from the air and descends to the bottom of the bottle. Once this mist has settled, envision removing the cork, start breathing in, and begin again.
As you repeat, work your way up to holding your breath for longer intervals (20 seconds, 30, and so on). You will get very warm within 15 minutes of doing this exercise. By utilizing this technique, even those who are chronically cold can generate enough body heat to stay comfortably warm for hours."
In the book Earth Qi Gong for Women by Tina Chunna Zhang she writes: Qi Gong Regulates the Functions of the Circulatory System. Qi gong does a good job of promoting efficient blood circulation. Unlike other exercises, qi gong creates energy through relaxed exercise without causing too much physical tension. This kind of soft movement can easily increase the blood circulation in the tips of the limbs, where there is normally less blood than in most other parts of the body. Many practitioners who have always complained of having cold hands and feet have found that qi gong effectively regulates the temperature in their limbs.
Qigong postures like Knocking on the Door of Life, Karate Chopping or Yi Jin Jing for the Hands should also help warm the hands by increasing energy and blood flow in the hands and fingers. Also by alternately clenching then relaxing your fists. Even a simple visualization of moving red light, fire energy, from your chest, down your arms, and out your fingers may help.