Please show gratitude to yourself for taking this time to commit to your own process in whichever way you wish to use it. To benefit from this commitment which you are making, I would invite you to set an intention to bring you to a point of focal clarity for the duration of this 21-day yoga practice. When your intention is clearer, the impact will be deeper. The impact of change is felt more strongly through our physical bodies than purely through our minds and thoughts. Intentions can change through the embodiment of time and action, and this is fine, let this happen if it does. However, find a starting intention for this practice, is an essential part of the process.
Follow each lesson from day to day - this is more effective than skipping lessons or jumping around.
Enjoy your practice.