This is something that I cannot emphasize enough. You have to be reading your own writing before you publish it. Please—for the love of all that is holy and unholy—read through your own writing.
This is something that was told to me in a workshop I was in over the last three months. I. Did. Not. Read. My. Work. I suffered for it. My writing was so full of problems it was ridiculous.
Reading through your work, preferably out loud, can bring a lot of issues to light. If you're confused whether to use a comma or period then read it out loud. If your worried that your writing might be clunky, which it likely will be without doing so, read it out loud.
Seriously though, by reading out loud you can determine a lot. When you do this you can realize when you use the same sentence structure repeatedly. I promise that that kind of thing is noticeable. You can change things up by making long sentences followed by short ones. Complicated compound sentences followed by dependent clauses(that can be another chapter), followed by short and sweet sentences.
The thing is, when you read your work before publishing it it is just better. You catch typos. You can vary sentence structure. All these things will make your writing better. Remember to leave a chapter comment for any writing or grammar related questions. I'll directly respond if it's short and make a chapter if it's more complicated.