Who will you practice this on first? Where? When?
Most people, including me, have the greatest challenge accepting the past without regret. What part of your past could you simply accept as being done, over, no longer capable of being changed in any way? The next step is seeing that past as making you who you are today. Every part of that past has contributed to who you are, even the parts that you might be ashamed of, or are still carrying hurt over. If you truly accept your past, AND you have confidence today, then there is no need for regret. Make peace with your past.