"If you never hit the word limit assigned to you by a teacher or editor; if anyone has ever called your prose "flabby"; if a critic condemned your first novel as being twice the desired length"...

...you need to read this superlative column by Roy Peter Clark of Poynter. (Poynter Online claims it has "everything you need to be a better journalist". I believe it.) And you will get even more helpful advice on writing tight by reading the transcript of the chat Clark conducted on Poynter — "How can I tighten up my writing?" is fascinating reading for both novice writers and experienced ones.