I think a couple of things that are always helpful, or have been to me, are that firstly the core storyline, that simple a plus b equals c, has to be clear, the outline and foundation that allows you to build and explore; if you want to submit to a publisher, your manuscript has to be as good as it can be at that stage of development and fit with the format they want; the editor is a collaborator and only wants your story to be the best it can be for you. Reading and learning from other authors is a must. Three of my go-to crime writers are Ken Bruen, James Lee Burke and Anne Cleeves.