Read a lot. Read every day. Read in lots of different genres.
Get a copy of Self Editing for Fiction Writers by Browne & King and Merriam-Webster's Guide to Punctuation and Style. Read them. Learn them. If you want to do this for real these are the tools you need. You wouldn't try to be a mechanic or a computer repair tech without having and knowing how to use the right tools. Writing is no different.