If you are not the best with punctuation or struggle a bit with some of the mechanics of writing, you have to get "The Elements of Style" by William Strunk and E. B. White. It is really a must have for every writer and poet out there. It is a very short book, only about 105 pages, and presents instruction that is very easy to understand and easily remembered. It is also a very good reference book to use when your stuck with punctuation or a tricky sentence you just can't seem to get right. I keep one on my desk at all times.