Research

Research is the key to good writing. If you just rely on what is in your head unless you are Einstein you will quickly exhaust your range of experiences of life.

If you are writing an essay at college for your professor you would not think of writing random thoughts from your head without looking up what the range of opinions about the subject are. research for a novel takes a different form. You have to look at locations, and understand that in different parts of the world ordinary things happen in a different way. You have to think about injuries for example and if you are writing about someone who has a broken back - what will the likely disability be? How long will they have had to spend in recovery/physiotherapy before they can begin to rebuild their life.
The Internet gives us so much information available instantly at our place of writing. But it does not replace proper reference books. there is something about flicking through a reference book about for example the city you are writing about that can stimulate the creative process and suggest all sorts of different angles for where the story will go.
There is nothing worse than reading a book where the research has been patchy and things just do not work. If you know London and someone comes out of Buckingham palace and after running for five minutes enters the tower of London then you will likely laugh at the ignorance and lack of research of the author however enthralling the plot.