Paul Brians' fantastic award-winning website by an English professor in Washington state is THE place to go to learn the finer points of English, which, as we all know, is the easiest language on Earth. (or should I say, "on the Earth"? Or simply, "on earth"?)
He has short but very useful explanations of usage questions like LOSE/LOOSE and many many more. Definatelydefinitlydefinetly ??? worth bookmarking!