Now the fun part, just sit down and write. Always start the first chapter in the middle of action. From then on try to have heat on every page (action). Leave out any idea or sentence that doesn't move you story along, and be careful when adding any back story. The back story should be adding sparingly , let it built through the novel. If you put too much too soon you will bore the reader, not a good idea.  Remember Conflict is King, there should be conflict with your characters from page one to the last chapter.  The conflict should build throughout the story, every time the reader thinks its safe throw in another twist. Also adding a sub story is fine just let it not take away from your main story.

I know you've hear this a million times...Show don't Tell. When writing, bring in all 5 senses to the story, what does the character feel, smell, hear, taste, etc. most important Watch Your POV!   Stick to one character's thought the entire chapter, if you don't it will confuse the reader and stop the storyline.

If you haven't noticed we're a busy world, we are use to getting everything we want fast. James Patterson, bless his heart started this Short Chapters. It's up to you but most readers including editors like short chapters like 8-12 pages instill of the traditional 30-40 pages. Being a nurse, I love the medical stuff, but most reader will flip past a 3 page autopsy, mine are brief, the characters get the info they need and their out of there.

I read my chapters out loud to myself as I go, this helps pick out errors and really helps me know if it just sounds right. When you're ready to let someone else review your work, give it to someone other than a close friend or relative. Why? You know grandma isn't going to say it'd awful. This may come as a surprise, but you "baby" will be edited several times. Even tossing it in a drawer and leaving it for a month or two, then going back you will pick up several editorial changes to make.  Writers groups are a good resource as well, just be prepared to hear criticism.
You should make an effort every day to write and read the genre you're interested in writing. Take note on how the masters write. Go to writing conferences, they are a gold mine of ideas and encouragement to all writers.