You probably had an English teacher at some point who sang the praises of a little white book titled The Elements of Style, often referred to by its authors, Strunk and White.
If you were forced to buy this book, I urge you to free yourself from its clutches. If someone recommends it, telling you it's a type of holy book for writers, politely say no thanks.
Strunk and White has more bad writing advice per page than almost any other book published. Follow it, and you'll hamper your style and become a weaker fundraising writer.
Not all of its advice is bad. "Write with nouns and verbs" is good.
But far too much of it is pointlessly bossy or just wrong: Like "Do not inject opinion." Really? What genre would that be?
Strunk and White's most damaging advice is "Use the active voice." Passive voice is the right voice in many situations. Especially in colloquial writing such as fundraising.
Then there's the fact that the book so often fails to follow its own advice. In the section urging writers to "Put statements in positive form," you read this sentence: "The adjective hasn't been built that can pull a weak or inaccurate noun out of a tight place." There you have it: A sentence in negative form, passive voice, and using three adjectives. It's not a bad sentence. But it's one you'd never write if you follow Strunk and White.
Whole generations of would-be writers have spent their careers wearing the Strunk and White straitjacket. Don't let that happen to you.
There are plenty of good sources of writing help. A standard stylebook, such as The Chicago Manual of Style gives solid advice and doesn't stray into bossiness. Or the excellent On Writing Well by William Zinsser, which is packed with real advice that can help strengthen your writing.
(For more on the problems with The Elements of Style, check out 50 Years of Stupid Grammar Advice.)