I often start with a concept for the ending and work backward.
I visualize characters in my mind, often based on people I know or have seen, so that I can be consistent in my descriptions of their physical attributes and personalities.
I fact check. If I mention actual locations, I have either been there or have researched the place extensively, including printing out pictures that I keep in front of me when describing locations to make them authentic.
I read and re-read my work to death, and I am a stickler for spelling, grammar and punctuation, so I not only edit myself, but I use tools such as spell checker.
I ask trusted, well-read others to preview my novel and offer feedback. Were the characters well-developed and interesting? Did the plot make sense? Did I overlook any grammatical or spelling errors? Did you like the ending? Etc. Etc. If I need to, I build from there.
Once I have a printed version, I edit it again. It's amazing how many times you can edit something on your PC and it still looks completely different in print.