How can I improve my English composition and rhetoric skills?

Question:

How can I improve my English composition and rhetoric skills?

I sincerely want to better myself intellectually by improving my composition and rhetoric skills. In middle school and high school, I scored exceptionally well on the FCAT Reading and Writing tests (that's Florida mandated exam which determines whether you get promoted to the next grade or in high school whether you receive your diploma). However, as I went through college aimlessly, I feel that my composition and rhetoric skills have waivered. I make C's in English and public speaking courses something that never happened prior to college. My essays are no longer praised, and I feel intellectually inferior compared to my peers in a subject that was once deemed my strongest. I wanted to make a career out of writing children's books, but now I am perfectly contempt with the business world as writing is no longer my forte. Please share with me your insight and experience. Offer up advice. Thank you in advance as your responses are greatly appreciated.

Best Answer - Chosen by Asker:

The best way to learn rhetoric is to go to the source...THE RHETORIC by Aristotle. As far as composition goes, a good handbook will get you going...but you need to write and practice every day.