Your average Tai Chi book seems perplexing to a beginner. In this article, I'd like to strip away all the esoteric notions and give you 4 simple instructions. Don't get me wrong, there's a time and place for the mystical but the basic concepts come first.
I'll admit, I've always been drawn to the far out and the magical and when I started learning Tai Chi I was surprised by the mundanity of it. It seemed to be much more about staying in the hips and keeping the knees in line, rather than moving balls of energy around. This is the best way to proceed and perhaps by perfecting the mechanical you may eventually experience the ineffable.
Relax. Relax, practice and practice relaxing. Whichever particular exercise or form you're doing, relaxation is of primary importance. Bring your mind into your body and if you perceive any tension let it go. Becoming softer should be your main focus, for a long time, because without relaxation there can be no Tai Chi. Even after many years, you may find tension previously hidden from you. Relaxation isn't an end in itself, it is fundamental to developing, rooting ability, speed and power, but if you achieve just one thing from practicing Tai Chi let it be relaxation.
Posture. You can't really understand Tai Chi's postural requirements without a teacher. Corrections need to be felt, remembered and gradually embodied. I can tell you to keep your knees in line with your toes, pull the waist back a little and sink into your hips but unless I show you what that means you are unlikely to get it. If you do see a teacher regularly, then perhaps concepts like hollowing the chest and rounding the shoulders will make some kind of sense but even then I wouldn't follow prescriptive instructions from a book. Correct posture is of utmost importance but what you need to do right now isn't the same as someone else and it will change over time too. Broadly speaking, however, you should be straight, not leaning to the side, head straight, knees in line with the toes and weight sunk into the legs, and you want to be 'in' the hips.
Sink. Remember when you were a child, a parent tried to pick you up and you made yourself as heavy as possible? You do? Good, that's sinking and it involves the mind as much as the body. Stand in the Zhang Zhuang posture and relax deeply, imagine everything sinking downwards. Over time you will develop a certain heaviness and an ability to root. When you push hands with a partner it becomes obvious to what degree you have attained this ability. The trouble is that unconsciously we tend to avoid pain and discomfort. When you stand try to sink into the pain, relax through it, endure the momentary discomfort and you will become stronger, more grounded and immovable.
Whole body movement. The more you relax, the more you can work on moving the whole body together as one. The arms never move independently. Try moving an arm in an isolated non Tai Chi way and then relax and use the whole body. The basic Silk reeling exercise is the best way to train whole body movement. Use as little strength as you can. Keep practicing and eventually, the arms will float.
And that's it. There are other details and other concepts but these 4 come first. Every tai chi practitioner I know is still working on these aspects of their practice.