I had a sentence in one of my stories from a few years ago that readers seemed to really like. Everyone who was kind enough to give my draft a read pointed out that sentence, and how it seemed a fair bit above the rest, how much better the whole story would be if only all, or at least a good deal more, of my sentences were up to the level of that one. But that's just it. Look at the sentence, determine what works about it, how its different from your other sentences, how those differences might be applied to some of your weaker sentences to elevate them. You can't use those techniques from the good sentence all the time, but they will help you with what you have, and they will help you moving forward. Then you'll write another great sentence and examining why its good will help you that much more. Or maybe you'll read a great sentence. Reading is probably the best advice I can give people who are trying to improve their writing. You want to know what works? Go see. Publishable material is, well, published. Read a few good books, and then you'll have loads more example sentences to study. You might see these great sentences, even one of your own, and feel discouraged. But any example of great writing is another example of how possible it is. There isn't any magic involved, and no one is born with a skill that they didn't also have to hone. With continued effort and determination you can bring yourself up to that level. Van Gogh was a terrible artist at first. He started out doing practice sketches from drawing manuals, and ended up being one of the finest painters in the world. In a letter to his brother Theo, while Van Gogh was just starting to get the hang of it, he wrote "what used to seem to me to be desperately impossible is now gradually becoming possible." It won't be easy to write, or do anything, at any of the highest levels, but if you have the dedication, it will gradually become possible.