Becoming too task oriented as well is a bit of trap. As you tick off lots of unimportant tasks, you pat yourself on the back on how effective you are. You risk adding more and more tasks without considering how they fit in with your goals. (This might be what unconsciously goes in the mind of students and writers when they spring clean their houses instead of writing or studying.) Having said that, having a plan that you then act on (and not ignore) is better than not accomplishing anything at all.

I'm not sure how easy a "Plan B" is. If you can anticipate the ways in which your plan fails, why not just incorporate them into "Plan A"? Alternatively I would suggest adding a little flexibility. Evaluating the outcome of your plans should help also. But I really like the "Granularize" and "Quantifying Results". I wish you had written this three months ago. It explains why I'm having so much trouble accomplishing a task. (Develop a marketing plan for an app to be specific.)

Additionally, I especially suffered analysis paralysis by chasing perfection. I'd spend hours shifting tasks around and feel guilty that I spent so much time not getting stuff done. It was for this reason that I built an app to automate my planning process. (Shamful Plug . Currently free for all LessWrong readers.) As a time saving device it's been ok, but it's real benefit is in knowing that I've committed to accomplishing certain tasks and being able to refer to the plan when I get behind or ahead. There's also nothing better than being able to add tasks at odd moments when they pop into your head, instead of sitting down later and thinking "what did I have to do again?".

So I'll finished then on an obvious note: Whatever process or tool you use, you need to record it and not rely on your memory. Because you're more likely to only remember the urgent tasks and delay the important ones.