Come up with a compelling premise. Stephen King says he writes most of his novels from a "What if?" model, such as what if a terrifying mad dog was stalking a person? The more compelling your premise, the more engaged you will be to sit down and write every day. The premise also should possess inherent conflict for the story. J.K. Rowling didn't just send Harry Potter to a wizardry school; she also exploited the conflict between wizards and Muggles.
Create characters with strong, primal goals, such as surviving a natural disaster or saving the life of a wife or child. The more primal the goal is for the protagonist, the more obstacles you can throw at him, because he must achieve the goal. This keeps your characters from becoming passive. And when creating the antagonist and other characters, try to give them goals diametrically opposed to the protagonist's, in order to create more conflict.
Outline your novel. Break it into three or four acts, depending on your story. This will be your blueprint, and while you might change elements when writing the book, the outline gives you a concrete structure you can refer to when working. It will keep you on track, remind you where you're heading and hopefully reduce the risk of spiraling down a pointless digression or route. The opening of the book also should start with action. Unpublished writers don't have the luxury of building up to the story, which should begin as late as possible to hook the reader.
Create a daily regimen. Stephen King suggests writing 1,000 words per day, and with this model, it would take 75 days to complete a 75,000-word novel. By breaking up the book into smaller increments, it helps to keep you from being overwhelmed by massive word count of a novel, forcing you to just focus on each day. Set specific times when you will write, and stick to them. If you have kids, you might want to schedule a couple of hours after they go to bed. The purpose is to figure out when you can fully focus on your writing.
Reward yourself for sticking to the routine. Unless you've already sold the book proposal to a publisher, there probably isn't anyone who really cares if you finish the novel or not, so you have to motivate yourself. A daily reward might be as simple as your favorite candy or dessert. Deprive yourself of the reward if you don't complete the day's work. And for completing the novel, promise yourself a big reward, such as a vacation or a new TV. Just make sure it's something you really want, so on days when you don't feel like writing, you can remind yourself of the pleasure you'll receive once you type "The End."