Do not, under any circumstances, start writing without an outline or other solid plan. If you do, you’ll spend forever untangling your mess of a novel. Your plot will make no sense, your characters will be flat and contradictory and you will have too many ill-explored themes. Revising this will frustrate the hell out of you and will lead to many bad life decisions and too much money spent on liquor.
Seriously, don’t start writing without an outline.
Don’t write your outline without a basic knowledge of plot structure and character arcs. I know things like plot structure seem boring and formulaic, but it’s good to have a handle on. Not to say that you need to follow the structural ‘rules’ of writing to the letter. However, you can’t break the rules without knowing them and understanding how they work.
Don’t edit or censor yourself as you go through the first draft. Let it all flow onto the page/document. Even if it feels like it’s becoming a mess despite your outline. Revising and editing will come later. Finish this draft first.
Don’t assume that others will understand your characters like you do. You may have a crystal-clear idea about who they are in your head, but does it show in your work?
Don’t start revising on a chapter by chapter basis. If you do, you’ll keep running into the same structural problems and pushing them back instead of solving them. Rather, start by looking at your draft as a whole. Does it have a consistent theme? Is there a logical sequence of events? Etc. After you’ve fixed the bigger issues, work your way down to the details.
Don’t procrastinate on revising by writing blog posts about writing novels.