Probably the most helpful tip I can give to authors is to read. I have two distinct ideas in mind.
First, read good books. I believe the biggest influence on our writing is our reading. Something about the way the brain works. Language seems to be learned by imitation. Think about how you learned to speak. Think about trying to learn a foreign language from a text book.
By the way, I’m not saying how-to books aren’t helpful. I’ve found them immeasurably so, but the best ones always give examples, and the really good ones give negative and positive examples.
But reading good books is only one way that reading can help writers to improve. The other is when an author reads his own work aloud. Something about hearing our work helps us find the good, the bad, and the intolerable that must be excised with tough-minded revision.