Hi, I'm a history teacher. Maybe I can help.
Your teacher is right. You should try to establish some criteria . Without knowing what the subject is, it's difficult to comment but definitely set out how you are going to evaluate something in the opening paragraph.
Secondly add nuance. Nuance is extra detail and/or analysis that helps you to avoid generalisations. So when it comes to significance consider short term vs long term - something could have little impact to start and then gradually become increasingly impactful. Also consider tangible vs intangible significance. So tangible refers to things you can measure..........unemployment came down, votes for a party went up, life expectancy increased...........anything you can measure. Intangible is more about what people think. Did the bombing of Dresden have a tangible impact on Germany........not particularly. Did it have an intangible impact.....yes, as it lowered morale.
Tell me what the area is and I might be able to help more.