Learning Tai ji
How to learn tai jiPractice, practice, practice
There is no substitute for practice. This does not mean that you spend hours at a time practicing. What it does mean is that you practice regularly. Set aside a set time for practice and get into a routine. That makes practicing so much easier
When practicing divide your time into "real" practice and "doing tai ji". By "doing tai ji" I mean doing the form with an awareness of the movements. Doing that means you can apply the lessons you learned. "Real" practice is time spent correcting errors and learning new movements and ideas. As well as strengthening the awareness and application of the principles.
Find a good teacher
You cannot learn tai ji from either videos or books. It requires that you find a teacher who knows the principles and can show how they are applied. A good teacher also challenges their students to do better. Often by example.
If you come across a teacher who claims their tai ji is the only "real tai ji" then run a mile. If you come across a teacher who never teaches about the principles of tai ji then also run a mile. In both cases the amount of tai ji you can learn from those teachers will be very limited. However if that is what you want to do then don't let this warning stop you. Just be aware you're not learning tai ji. You're just learning a bunch of movements.
Apply what you learn
This is one of the reasons it is necessary to find a good teacher. Such a teacher can show the application of the principles as well as the moves. Tai ji is as much a martial art as an exercise regime. This means that, even if you have no intention of ever using it as a martial art, you can still develop an awareness of how the movements can be used. This puts substance into the form and provides a source of understanding that improves timing.
Eventually you should expect to start learning the partner drills. These help the development of sensitivity to what the other person is doing - listening. As a result you can learn how the various movements, and positions, in the form work when dealing with another person.