Typically, I write out my plans. I have a three-month plan, a one-year plan, and a "where I want to be in five years (maybe possibly)" projection. (The latter doesn't rise all the way to a plan because life's too unpredictable to plan that far ahead). I also do an annual check-up on all my plans, usually on or about January 1 of every year.
That probably makes me sound like some kind of obsessive nut. (I won't deny that.)
But, in reality, I'm actually quite flexible. My obsessive planning weaves not a linear road map but a safety net for me. Rather than a hard-and-fast rule to follow no matter what happens, my plans typically only come into play if no better options present themselves. For example, a number of years ago I taught a class. Every week, I would write out at least one lesson plan; often, I would write out a backup plan, too. In more than six years of teaching that class, I think I actually used my lesson plans three or for times, and they were probably the worst classes I taught. Instead, I walked into class every week (armed with a backup plan) and threw myself into the spirit of the moment, letting the class happen.
My life-planning is like that, too. When I look back over my annual checkups for the last decade or so, I find that where I end up and where I expected to be are almost always very far apart. I hardly ever actually follow my plan, because Life usually offers me a more interesting option.
While it may be a weird way to live, I think this tendency has helped me as a writer. For one thing, I have a lifetime of imagining alternative scenarios for virtually every situation, which helps with plotting and character development. More importantly, however, I think is the ability to let go of the plan when it is time to just fly. The trick is balancing the need for security with the desire to march off into the unknown.
**laughing and awestruck by a moment of pure serendipity**
I looked up the quote I planned to end this with, and discovered that whole verse of the song is even more appropriate than the single line itself:
Before you cross the street
Take my hand
Life is what happens to you
While you're busy making other plans
"Beautiful Boy (Darling Boy)" by John Lennon