One possible version:
Dear Erin,
Thank you for your letter. I can offer you some useful suggestions.
Homework is very important. You can’t do well in your exams without doing your homework. I think you should plan your time carefully. You’d better make a list of all the homework you have to do, and make sure how much time you need to finish it all. While you’re working, you must concentrate on your study. Of course, in the spare time you can do something interesting to make yourself relaxed.
I hope my suggestions will give you some help.
Yours,
Amy
略