#1 STAY FOCUSED
There's always, always something that can distract you from sitting in your writing chair. The grandkids want you to go play in the snow. The doughnut in the kitchen is calling your name. It takes a lot of self discipline to get a book written. You are your own boss, so you have to keep reminding yourself that if you don't get a book written, you are not going to get it published.
#2 NOTEBOOK, FILE, SOMETHING
Keep a notebook, file or something to refer back to concerning your characters. If Tommy has brown eyes on page four, blue eyes on page sixty and brown eyes on page two hundred, your readers will scream at you. I'm old school. I still use a notebook and a pen for my rough outline ideas. On the first page of that notebook I write the ABC's down one side, and then I start a list of my characters. You really shouldn't have characters with the same first initial. It's confusing to your reader. Also hero/heroine with sound alike names (Lisa and Lane) will stump your reader. Especially on series books when I need to remember the hero from book one when I'm writing book seven, I buy one of those little recipe card files and keep it right beside my computer. Each character, even the dogs and cats, gets an index card (filed alphabetically by first name) in the card box. That way all I have to do is find the card, and presto hero in number one was six feet two inches tall and had blue eyes. Some folks like to do this on the computer, and that's fine, but once I lost nine thousand words by shutting the wrong window and not saving. So it's old school for me.
#3 EDIT! EDIT! EDIT!
Your rough draft is finished. Now it's time to edit, edit, edit. Have someone else read your manuscript, and don't take the constructive criticism personal.
#4 WALK AWAY
If you begin to feel overwhelmed while you're working on those edits, get up and walk away from them. That's when it's all right to leave the writing chair. Take a walk. Pet the cat. Get your mind cleared so you can go back to the edits with a fresh outlook.
#5 START A NEW BOOK
Your book is finished, is in the agent's hands or the publisher's, now what? You start another book! This is the WRITE, DON'T WHINE! phase. Don't whine that it's taking so long to get your book published, or that you've got rejection slips. Write another book while you're waiting. When that first one does sell, you'll have a new one in your hands to sell.