When your life is already busy, the idea of trying to add a novel project to the mix can sound crazy--if not impossible. I won't lie to you and say that it's easy, but I will say that it's worthwhile if creating a book or series of books is your dream. Here are some tips that I've found helpful:
Budget willing, having your own computer and dedicated space to write will give you consistency and stability that will show in your writing. I've done some book chapters while traveling, but long-term it's good to have a "home" where all your research materials and main book file are within easy access. (If you're unable to do this and need to share information across multiple computers, a USB flash drive can help you keep everything organized. They make great back-ups, too.)
If sitting in front of a blank computer screen gives you writer's block, I've found that carrying around a notebook (now upgraded to a notepad app on my phone) and going somewhere with background noise has helped in plotting out individual chapters. Music can help as well--sometimes a good song can trigger the mood of an entire scene, and I pay attention to this as I'm listening to the radio throughout the day.
A lot of this is going to be based on your personality, so there's going to be some trial-and-error on what works best for your creativity.
Time is your most precious asset--how you spend it or invest it does matter. Sometimes that means being different from most people. For example, the average person in America watches about 21-28 hours of television a week. I was a broadcasting major and like television, but to get my books done I had to cut back. When I do watch television shows and movies, I do it actively--enjoying them but also looking at how they work from a story standpoint.
Sometimes you may have to say no to opportunities that aren't bad but are going to take too much of your time. This is harder in the beginning, but over time people around you begin to understand that getting your novel completed has a priority in your life.
Creating a System
There are several ways you can break down a novel into smaller projects you can manage without feeling overwhelmed. When setting up my series, I spent a lot of time on preparation--getting the characters, setting, and overall plot (not necessarily all the details but key points) developed before I started chapter one of the first book. Long-term, the extra time in that stage has saved me time in all the others.
I treat each individual chapter like a scene in a television show or movie, knowing before I begin writing where I need to end up. There's a lot of freedom in the middle to try out new ideas and build more interaction between the characters, and the goal isn't to just breeze through the chapter as fast as possible--though sometimes you'll get a good flow that will work out that way.
Two books that can help you with this are Make a Scene by Jordan Rosenfeld and Story Structure Architect by Victoria Lynn Schmidt.
Dealing With Distractions
Not all interruptions are bad things--a great example (as if on cue) is our foster greyhound Tatiana (a.k.a. "Tater Tot') letting me know she wants to play by laying her head across my arms as I'm trying to type this. If you're writing for long stretches at a time, it's easy to forget to take breaks--so in this particular case it's an accepted and welcomed situation.
If you're constantly getting interrupted however, you may want to try writing either very early in the morning or very late at night. This may require some adjustment at first but may help you be more productive in the long run. I alternate with this, since not getting enough sleep over time can wear down your creativity, too.
When Things Get Tough
Sometimes a life circumstance can knock you down to the point you may not feel like writing at all. When my family found out my younger brother Chris had cancer earlier this year, by coincidence I was right in the middle of a set of fictional scenes dealing with a similar situation. I felt like deleting the entire book at first because I couldn't bring myself to even review what I'd already written--much less keep going with it. Now that I've had some time to work through the situation, the resolve has come back to finish what I've started--and I'm glad I didn't give up.
Integrating Writing Into Your Daily Life
Before I started writing novels, I wrote short stories and articles for about three years (the first year was for free--not realizing I could make some income from it). I'm a member of a handful of online writing communities, the primary two being Gather and Writing.com. It's good to get around people with like interests, and the Internet has created an opportunity for writers that previous generations probably couldn't have imagined. Being in a constant state of educating yourself on new things and developing good habits are important in transitioning writing from a hobby to a career.
I think this is very important to mention because there needs to be joy in what you're doing. I love the process of writing a book, and it's something I want to keep doing again and again for the rest of my life. When you find something that does that for you, don't let it go.