The writing style which is most natural for you is bound to echo the speech you heard when a child. English was Conrad’s third language, and much that seems piquant in his use of English was no doubt colored by his first language, which was Polish. And lucky indeed is the writer who has grown up in Ireland, for the English spoken there is so amusing and musical. I myself grew up in Indianapolis, where common speech sounds like a band saw cutting galvanized tin, and employs a vocabulary as unornamental as a monkey wrench.
Vonnegut’s advice is great and echos advice I’ve heard about/from other writers like Hemingway and Stephen King.
The pieces of advice that have helped me the most have been on keeping things simple and writing like myself. No matter the size of the post on this site, I usually reread them at least 5-10 times, each time paying attention to where I can eliminate redundancies and gain more clarity in the idea being conveyed.