E.E. Cummings may have eschewed punctuation and capitalization, but you do so at your peril. When you write, you communicate, and if readers can't make out what you're trying to say because your sentences run into each other, they'll give up and move on. Grammar and spelling—equally important. So whether you are composing a book, a brochure, a blog, or even a note to your kid's teacher, write it right because you won't get a second chance to create a first impression. Make friends with your dictionary. And if you have time, get friendly with one or several of the following resources:
For serious answers to ponderous questions, try The Chicago Manual of Style. Another good resource, especially when writing press releases, is the AP Stylebook. Both are available online through subscription. If you do buy hard copy, make sure you get the most recent edition of these or any style guides because, despite what you may have learned in school, the rules do change.