1 My first rule was given to me by TH White, author of The Sword in the Stone and other Arthurian fantasies and was: Read. Read everything you can lay hands on. I always advise people who want to write a fantasy or science fiction or romance to stop reading everything in those genres and start reading everything else from Bunyan to Byatt.
2 Find an author you admire (mine was Conrad) and copy their plots and characters in order to tell your own story, just as people learn to draw and paint by copying the masters.
3 Introduce your main characters and themes in the first third of your novel.
4 If you are writing a plot-driven genre novel make sure all your major themes/plot elements are introduced in the first third, which you can call the introduction.
5 Develop your themes and characters in your second third, the development.
6 Resolve your themes, mysteries and so on in the final third, the resolution.
7 For a good melodrama study the famous "Lester Dent master plot formula" which you can find online. It was written to show how to write a short story for the pulps, but can be adapted successfully for most stories of any length or genre.
8 If possible have something going on while you have your characters delivering exposition or philosophising. This helps retain dramatic tension.
9 Carrot and stick – have protagonists pursued (by an obsession or a villain) and pursuing (idea, object, person, mystery).
10 Ignore all proferred rules and create your own, suitable for what you want to say.