Answer:
proudest moments to choose, getting a reward, graduating elementary school/middle school/highschool, working towards something and finally getting it, getting your first pet, getting a A or B In a class. You can also just make something up if you can't remember any proud moments, choose something vague but something you would be proud of
Step-by-step explanation:
one of my proudest moments is.... This specifically is one of my proudest moments because I worked very hard towards {Insert proudest moment}. How I got to this proud moment is by working very hard. Why I am proud of myself for accomplishing this goal is because it made me happy and one more step towards accomplishing other goals. This is why I am proud of myself for this (moment).
Hope this outline helps, change it to fit with whatever proud moment you choose.