The first step starts with yoga – free yourself from the idea that you can be either “good” or “bad” at yoga. There is no such thing. What you bring to the mat is what you are. It’s called a yoga practice, from your first class to your ten thousandth.
Secondly, liberate yourself from any idea regarding the amount of or types of poses you can do. If sukhasana, or easy pose, was the only pose you ever did and you remained mindful of the breath, you are neither “better” or “worse” than the yogi throwing their leg behind their head.
Third, give yourself room both in your poses and your daily life to be free of self-judgment. When the urge to criticize yourself arises, make sure that you can breathe. Then, be sure to ease tension in the body (common areas are face, shoulders, and hips/low back). Let the action, pose, or moment stay in the past and focus on now. From moment to moment, focus on anything happening that can keep you in the moment – the best default is the breath, as that should never stop.
If you need to go back to re-evaluate the past moment, do so later after giving yourself some distance. It’s the same concept as coming back to a mathematical problem, term paper, or disagreement with a partner after some time away so as to approach the solution with a fresh mind.
This is my version of tapas + ahimsa, or the disciplined use of energy to engage in non-violence, in this case towards the self. You only have so much prana, or life force, to use each day – utilize it to focus on the now, and to use a clear mind to help solve problems in the past. In the meantime, being too harsh on yourself will cloud your ability to treat yourself fairly and to give yourself room to breathe.