The following guidelines are easier for some to follow than for others, but they can, with a little work, be learned by almost anyone. Once learned, they'll become part of your permanent knowledge base like the multiplication tables or your best friend's phone number. You won't have to learn them twice. 

Take time then, even it you're fairly confident    about your grammar, to see if you need to work on any of these six areas. If you do, try to understand the logic of the rule, what its purpose is.

... see if you need to work on any of these six areas.

Study the examples until you see how the rule is violated and how it can be set right. Work the activities until you've mastered the rule. Notice which areas are most problematic for you personally. Finally, make the carryover into your own writing. When you do that, you can consider the rule learned.