If possible, set a specific time for writing each day. Let people know you don’t want to be disturbed during this time, unless there’s an emergency. Keep distractions to the minimum, background music is fine. Don’t open your browser unless you really need to look something up for what you are writing.
Set a reasonable goal each day. Two hundred words, five hundred words, a thousand words. Select something you feel comfortable doing. Going over the limit you set is fine.
Write every day. It doesn’t matter if what you write has nothing to do with your book. Get into the habit of sitting down and putting something on paper or the computer.
Join a writing group, Being an author is a lonely life, and interacting with others who are of like mind will help tremendously. Check your local library or college for writing groups, also check Facebook. There are a number of good groups on FB. Writers World is a great one for critiques of your work and the lessons on writing you can find there.