One of the components of yoga is svadyaya, or self-study. This refers to "self-study" on all levels of our being, but here I'm discussing this concept in relation to our practice of the asanas, or yoga poses.
When you're new to the practice of the yoga asanas, you depend on the teacher (or a video or a book) to tell you where and how to place the different parts of the body for the poses you're practicing. You're given basic instructions for how to open and extend different parts of the body and how to create more mobility, stability, and balance. When you become more experienced, you'll learn to "fine-tune" the poses, bringing your body into a healthier alignment with more ease.
The teacher continues to give you guidance in the poses for as long as you're taking classes, but you also need to figure out for yourself how you have to work to improve your own poses. This is where svadyaya comes in (as well as dedicated practice!).
Early on you'll figure out what kinds of poses are difficult for you and what poses are easier. Repeated effort and practice will help you to improve, but you'll probably still experience that you remain "stuck" in certain kinds of poses.
This is where you have to start observing in your own body what's going on, and take steps to change it.
For instance, if back-bending poses are difficult for you, start to figure out where in your own body you're stuck. The shoulders may be stiff and the mid and upper back may be stiff, while the low back may hurt because it's doing most of the "bending". Recall what poses, what instructions, and what props your teacher has suggested for moving into a better backbend. Were you given specific instructions for your own body that helped you in class? Are you practicing them at home? Or remembering these instructions next time you come to class, even if the teacher doesn't mention them?
Also pay attention to your own body -- can you figure out what parts are maybe moving too much, or not enough? Does one side of the body work differently than the other? Is there more awareness in some parts of the body than in others? Does part of the body work harder than the other? Can you figure out what are the simpler poses/stretches that will help you move in the right direction? Much of this self-study has to be done during your own practice, partly taken from what you've learned in class, and partly from what you've experimented with yourself.
This is a never-ending but fascinating process! I hope it also remains a fun, playful process for you as well. It takes time, patience, and effort, but you'll find that it's a very satisfying experience!
Photo by Mrityunjaya Yoga Studio, Creative Commons License 2.0