I've said it before and I'm saying it again: don't waste words. It was Polonius of Shakespeare's Hamlet who said, "brevity is the soul of wit." His words weren't far from the truth.
Don't get me wrong, you can write a story of any length without wasting words. Robert Jordan was a master of writing weighty tomes virtually devoid of extraneous ink. As long as every sentence serves at least one purpose and the majority serve more than one, you're on the right track.
Any sentence that doesn't move the plot forward, develop characters, reveal setting, provide comical relief, foreshadow, or drastically change the mood of the scene is a waste of words. Luckily, many sentences do at least one of those things. Words are most-often wasted when describing something. Here is an example:
Thomas led his band of bards down the main avenue of the city. Vendors hawked their wares on both sides of the street. A few dogs crept out of an alley, their fur matted and shaggy. Thomas smiled broadly at a woman walking in the other direction, her eyes lined with thick, garish black paint. She regarded him coldly.
The first sentence of the example pushes the plot forward. If this was the first paragraph of a manuscript you could say that it also gives a hint at the characters. Sentence two provides a small piece of setting information. The following sentence is probably, for the most part, a waste of words. It gives a minuscule sense of setting, but not enough to include it in the story unless it shall prove important later on. Adverb aside, the fourth sentence is passable. It gives a sense of Thomas' character and possibly foreshadows. The second part of the sentence can be cut if it never ties in with character or setting. One of the adjectives is an easy snip in any case. The final sentence's fate depends upon the rest of the story. Do women generally resent Thomas at first? Will this woman prove important later on? If the answer to at least one of these questions is "yes," then it's okay. If not, it's most likely a waste of words.
Keep in mind, this is an opinionated subject. Some people prefer extra description, making certain sentences useful rather than wasteful. That's the biggest exception. Know your audience before taking my advice into account.
In any case, the principle of "don't waste words" rings true. The tough part is trying to effectively define "waste..."