One area of practice that is a problem for students, is making transitions from one form to the next in their Single Form or Long Form practice. While doing a single form repeatedly, it is easy to keep the flow, but then changing to the next form often results in an interruption in the flow. The same happens in the Long Form, where each change of posture can result in an interruption of the flow.
First it is very important that you keep your mind very calm, and concentrated on the flow itself. Too often during the transition, the mind ends up concentrating on the physical motion as the change from one form to the next is made. When practicing single forms, you have the time to establish a flow in the form you are working on, which is why you do Single Form practice to start with. As you go to the next form, let the energy flow smoothly into the next form, making sure not to drop down to the physical level. Take your time and learn how you need to adjust the energy to flow smoothly into the next form.
You can use the Long Form to help you figure out where your transition problems are. Anywhere in the Long Form you find that you lose the flow is a sign that you need to work more on that particular transition. That may also be a form that you need to apply more Single Form practice to. Take the transition and practice changing between the two forms where you are having the problem over and over, until they become second nature. Remember that the whole point of doing the Long Form is to get to the point that it just feels like one long form to you, with the flow uninterrupted, rather than a series of postures.
This all requires that you are going by feeling rather than thinking. You have to really be using the flow of the energy as your guide, rather than thinking about physical motions. You have to learn each form well and practice it over and over until you really understand the flow in the form. Then you have to feel what changes will have to be made to the flow in order to go smoothly into the next form without any breaks. Remember your Taichi Classics, "Continuous, allowing no interruption." Any time you loose that feeling of flow, you are not practicing on an energetic level.
Quality should always be foremost over quantity. In order to flow and transition smoothly, you have to really know each form well. Too many students are in a rush to learn the Long Form as quickly as possible, and as a result, really do not understand the single forms well enough to be able to establish a really good flow, let alone make smooth transitions. The Long Form then just ends up being a string of physical postures rather than a study in Taichi energy flow. The time you spend learning each form, if done properly will pay huge dividends with respect to flow and smooth transitions. Remember, make the forms second nature, no thought, just feeling.
Really focus in on this transition practice as it is every bit as important as the forms themselves. Two Person practice, such as Roll Hands, Four Forms, and Da Lu all rely on the ability to transition smoothly in the context of a constantly changing direction of flow. You must be able to adapt to where your partner sends the flow and follow smoothly, without conflict. This all starts with learning in your own practice to make smooth transitions.