If you would like to improve your writing, these are the resources I recommend as a starting point.
To get feedback on your writing and develop awareness of the kinds of mistakes you commonly make, I recommend spending some time critiquing other people’s work and having them critique yours in turn. I use Scribophile, which is free to use and has a very friendly, supportive community of writers. Other critiquing sites are available.
While critiquing will help you improve your writing at the level of scenes and chapters, you need beta readers to tell you if your novel is working as a whole. A beta reader is someone who reads a draft of your novel and points out any problems from the point of view of a reader. You can ask a friend to be a beta reader, if you trust them to be honest. Or you may find fellow writers who are willing to beta read in exchange for your help with their manuscript.