做好热身准备 Be Sure to Warmup.
This is very important: To have your body parts and muscles to be ready.
练习气沉丹田 Try to pass your weight to your feet, especially when doing bow stance.
This is to avoid hurting your knees: The idea is to let your feet hold your weight, and your legs supporting your posture, so your upperbody can rest on them and your hips can be flexible to move freely. For the leg that is having bow stance, let the foot align the same directions of the leg, and do not allow the knee go beyond the tip of the foot, the minimum angle of this knee between upper leg and lower leg is 90 degree, don’t go beyond that. The ending posture of 斜行 is a good example: while you are leaning forward to your left with most of your weight on your left leg/foot, which has the bow stance, keep your knee within the range of the vertical line of the left foot, while your right leg is behind you, you still need to let it support you by opening up your thigh and pass about one third of your weight to that foot. If muscles in your legs are not built strong enough, or you feel knees hurt, then stand up a little bit until you feel comfortable and can control your legs.
喝热水 To drink hot water during and right after practices.
This is common sense in Chinese culture. The idea is: your body’s temperature is 98 F, if you drink water with room temperature, your internal muscles have to do extra work to warm it up. While practicing Taichi, those muscles have worked hard and are getting tired and need to rest, so you don’t want to put extra pressure onto them. If you really prefer room temperature water, then drink it after your body is cooled down. The same concept includes cold foods as well. Forget about ice water.