My writing style drastically changed after taking a high school course focused on grammar and the English syntax. My advice is to use grammarly if you are just starting out, but think of expanding your knowledge about the English lexicon by buying a book about grammar and sentence structure. As while many might claim that grammar doesn’t make or break a story, it can definitely refine and define it. I found that by learning grammar from the ground up drastically helped by writing as it helped me understand flow, reason, and tact. A recommended book that I had to study during my class is Eats, Shoots & Leaves: A Zero Tolerance Approach To Punctuation by Lynne Truss.
Trust me, learning from the ground up and investing your time into writing rather than letting it linger will drastically impact your writing style. Make an active effort, and even if it’s not through a formalized learning, simple YouTube videos are enough. Some of my favorite sites to use to understand grammar are OwlPurdue and the MLA official website. Though these are used for formal writing, I go by the standard that you should learn formal before informal, as it is a stepping stone that we come across in every way, such as in maths, languages, and science.
Learn the theory before you practice.