One of the great things about being a writer is that you have the best excuse in the world to indulge your creativity and daydream at will (make sure you have a good stock answer for when the boss catches you staring off in to space like a space zombie from the planet Threnk though!).
Not an idle moment needs to pass that can't be filled with mystery, romance, intrigue and adventure. The ultimate time filler if ever there was one!
If you're like me, thinking about writing can be performed just about anywhere and often alongside any other task. Boiling an egg and making toast for breakfast? Those few minutes can be filled with plotting and character studies. Driving in to work for the daily grind? How might one of your characters approach this? If all else fails you can tune the radio to a news channel and entertain yourself on a daily basis with the most bizarre and ironic snippets going.
The point is that all of this can be done almost at any time or place. But what happens when you're doing this and the fabled (and undoubtedly fictitious) muse doth strike? You know the scenario; you're five chapters in to what is going to be your best work ever and suddenly, BAM! There's this really neat idea for a story about a woman who grows Chrysanthemums while fighting off the Forces of Darkness(tm) while holding down a steady and meaningful relationship and raising three kids (one adopted).
Do you drop the current work? Do you stick at it and forget the Crysanth lady? Oh my ducats, my daughter!
Well the answer I have for you is simple. You do both!
First off, you whip out your handy writer's notebook and pen that you always carry with you (you DO always carry a notebook and pen, don't you?). Then you spend five or ten minutes scribbling down absolutely as much as you can about your new idea, it doesn't have to be formatted, it doesn't have to really make sense, it doesn't have to be organised. Just literally a core dump of everything about the idea that's currently in your head.
After you've done that you put your notebook down and get yourself a large hot chocolate (or whatever you prefer) to celebrate. Celebrate what I hear you ask? That's easy, you have just successfully catched yourself one honest-to-goodness, live in-the-flesh, genuine, fresh idea. What's more, you'll never lose that idea and will be able to return to it at any point in future.
Now go back to finishing your novel that you're five chapters into. After all, the most important thing for a writer is to finish!
Using this technique I have currently dozens of ideas all freshly caught and shrink-wrapped waiting for me to have time to get to them. Sometimes I seem to have so many ideas that I couldn't write them all even if I were able to do it full time.
That's a story that will have to wait for another day though.