B.K.S. Iyengar, Light on Life, p. 56: "Long uninterrupted practice of asana and pranayama, done with awareness, makes the foundation firm and brings success. The young, the old, the extremely aged, even the sick and the infirm obtain perfection in yoga by constant practice. Success will come to the person who practices. Success in yoga is not obtained by the mere reading of sacred texts. These are increasingly essential aids but without practice remain simply theoretical. The test of a philosophy is whether it is applicable and even more so applicable now in how you live your life. Even Patanjali, who was born a spiritual genius, said that yoga is mastered only by long persistent nonstop practice, with zeal and determination."
At a loss for what to practice?
Practice what you know. If you are not ready for the last 4 poses, stick with the first 6 to build strength.