Rule #1 is: 500 words/day. 

Nothing happens unless you do this one.  It's the sine qua non bedrock of getting a novel done.  

Writing a novel is a long slog.  If you don't keep after it, it will get away from you.  Novel writing is a not a burst of inspiration.  It's a lifestyle.   

You can write more than 500 words.  Stephen King locked himself in his writing room in the morning and didn't come out until he had 1,000 words.  When he was young, on good days, he said he might finish up in a couple of hours, done by 10 am.  As he got older, he could be stuck in there until 1 or 2 in the afternoon.  

What happens when you write 500 words/day?

500 words = 2 typewritten double-spaced pages
500 * 5 days/week = 2,500 words, or 10 pages
10 pages * 4 weeks/month = 40 pages
40 pages * 12 months/year = 480 pages

The pages will accumulate.  
You will learn to write better.
You will explore blind alleys.
You will write a lot of boring stuff.
You will be proud of your progress.
You will finish your book.  

Let's talk about a few of those things.

You will learn to write better.
You get better at things you practice, and if you want to get better at writing, you have to write.  But it's also true because most writers get at least some of their great ideas while writing.  You've got George and Caitlin walking on the beach and they've had their conversation about Mabel.  But now what?  Well, there's a boathouse down there.... and we've already established that Mabel's friend Susan is always swimming... Susan in the boathouse... Susan eavesdropping...  And now you know how Mabel finds out about George's betrayal.  

You will explore blind alleys.
I don't know if he did it on purpose, but Roger Zelazny said he always wrote scenes for his characters that never made it into his novels.  I don't do that on purpose, but I've written whole sections of novels that just didn't work for some reason or other.  For a time travel novel called The Longest Tuesday, I spent eight weeks writing a long section about time travel to America before Columbus, then chucked the whole thing.  A lot of research went into that section as well as the weeks of writing.  But you know... some of it was just dull.  I might have fixed it, but it hit the cutting room floor because the overall story worked better without it.  That will happen to you.  Don't worry about it.  Maybe some of it will come in handy later, so don't throw it away.  You might use it in your next novel.  

You will write a lot of boring stuff.
Just like with a lover, not every moment is a life-altering moment of exaltation.  No matter how talented you are, some days you finish a little section, look it over, and are shocked at how dull it is.  It happens.  Sometimes those pages end up cut, sometimes the dull 1,500 words you just finished can be distilled into a sentence (the three days writing you spent getting Marge and Jack across the city can be replaced with, "When they got to Lansdowne station").  Sometimes you can save the scene by introducing another character (What if the lifeless Hector and William heart to heart is interrupted by Uncle Bob, spitting with rage over a referee's call that cost him a $200 bet?).  Sometimes it's a point of view problem - the narrator needs to be more detached, more engaged, or instead of how Srinivas feels you need to rewrite from Samson's perspective.  You'll figure all that out once you've got a first draft.  Don't worry about the boring parts, keep moving.  

You will finish your book.
Getting the first draft done is your goal.  Don't worry about how good or bad any particular day's 500 words are.  There's plenty of time for revision, and I'll give some thoughts on that later.  The important thing is to keep your project moving forward.  You do that by giving yourself a target and hitting it.  

It's the most important rule.