I was always taught to reflect back on lessons after completely executing them. I have stayed faithful to this tip, and by doing so I have learned a great deal about myself, my teaching, my students, and my lessons. In order to improve and assess lessons I use this lesson reflection document.
This document allows you to list the pros and cons of each lesson. When I file away my lessons for the next year, I fill this form out completely and file it with the lesson plan (The matching lesson plan layout is also in my TpT store!) and then the next year I am able to remember how I can improve my lesson, so that mistakes aren't made twice, and my approach continuously improves.