The first and final rule of quality writing is this: what doesn't strengthen your writing, weakens it.
There are no neutral words when you're trying to be persuasive - every word must be doing real work and every sentence must be necessary. Don't say in two sentences what you can say in one; don't use five words when you can use three. Don't use a five-syllable word when an available two-syllable word means the same thing. Take the fluff out of your writing.
Fluff is the often subtle cancer that grows - and ultimately kills - good writing. If your writing isn't achieving the effects you want, consider a few of the warning signs of a fluff infection:
Redundancy. Analyze your writing for places where you are repeating yourself. It happens often, particularly when the writer isn't convinced that the reader will get the point without it. Give your reader some credit. Make each point once and make it effectively - and then don't make it again.
Tangents. A good piece of writing is one that makes a single effective point, supported by other lesser ones; anything that doesn't directly contribute to that support structure is a distraction and an excuse to stop reading. Don't take readers on side trips and don't let them catch their breath. Cut out anything that doesn't directly advance the final cause.
Ornamentation. Ornamentation happens when a writer is hit with a sudden burst of creativity, and the writing ends up saddled with clever turns of phrase that don't contribute anything but wit. This is what Hemingway was referring to when he advised writers to kill their darlings - art is all well and good, but make sure it keeps its day job.
Pointless modifiers. Adverbs (words that modify verbs) and adjectives (words that modify nouns) are a little like salt and pepper - useful in very small doses, very bad in big ones. They're often used by lazy writers in an attempt to convince generic nouns ("the beautiful, voluptuous woman") and verbs ("he ran very quickly") to do more interesting jobs. The English language is full of precision nouns and verbs; whenever possible, use the right words rather than trying to modify the wrong ones.
Needless qualifiers and hedging. Phrases like "and yet, on balance" and "it could be considered"
destroy more confidence than they create.
Be direct and write with strength: boldly write what you know, and leave out what you don't.
Pretentious language. Occasionally, we all have a crisis of confidence that leads us to think that we need large words and cumbersome sentences in order to be taken seriously. This is when it is time to take a nap and let the feeling pass; "extraneous solutions that minimally impact positive budget modifications" is never going to sound better than "it won't work because it costs more than it'll make back".