Okay, my essential grammar tip is actually a website, Mignon Fogarty's amazingly useful Grammar Girl podcast website, to be precise. There you can find fascinating - but useful! - podcast topics such as Why Isn't Gruntled a Word?, Is Funnest a Word? and my particular favorite, The Apostrophe Catastrophe, Parts One and Two.
Refresh your limited knowledge (by the looks of a few of those query letters) of Misplaced Modifiers! Thrill to the confusion of Yoda grammar! And share in the triumph of Less vs. Fewer!
(Or you could just go read them to learn how to write better sentences. Just sayin'.)