What disciplines/habits are used to stay focussed on one novel over a long period of time?

One of my biggest issues is staying focussed on a single novel.

My imagination is always creating new and wonderful ideas. I write a few chapters on this story, a few on that story, but never finish.

What disciplines / habits can I put into place to stay focussed and finish a single novel?

Answer

1) So, don't. Keep several books going at once. What's stopping you? Maybe you need to switch gears often to keep yourself fresh.

2) Write short stories. Easier to finish in a bite.

3) Write an outline of your novel. When you get bored working on IIA3d, move to IVE12c. Jump around within the book and write scenes.