Pick a time of day to write for at least 20 minutes and read at least a chapter of a book each day. You have to develop the habit of writing and you have to know what good and bad writing sounds like, how it's structured, and how characters, settings, and plot are developed.
Second you have to find a good writing and critique partner. Your writing partner is usually someone who can keep you accountable and you can work out ideas with. They may or may not also be your critique partner. Critique partners can look at your work with a objective eye. You want someone who is both a reader and understands plot and character development. If you are fortunate enough to be able to hire a developmental editor, do your research and go for it.