Here’s a fellow writer’s grammar cheatsheet:
Common Writing Challenges for Native and Non-Native English Speakers, Grammar Cheatsheet.
Don’t forget to scroll all the way down to
Principle vs principal
I see that one misused often. They also include such gems as fewer versus less – a GMAT issue!! Grammar is a set of guidelines to make writing more clear. There are fewer “rules” than you might imagine. But there are several guidelines with various degrees of implementation.
Better writing stems from more clear thinking.