I learned about The Board back in college and I still use this in the office as my main task manager tool.  I like to keep things simple and that is why I continue to use it.  The idea is to be guided on which ones to work first based on importance and/or urgency.

Important + Urgent

You will want to work on the tasks that are on the left side of the grid and, naturally, the one at the top left being more of importance.  You will want to "kill" first the tasks in the top-left because these are the ones you are considering as super-important-the-world-will-freeze-over-if-you-don't-do-them kinds of tasks.

Not important + Urgent

The ones on the bottom-left, although are not that important, ought to be considered included in your priorities because of their urgency.  In the office setting, these could range from admin tasks that don't make sense how they play a role in the bigger picture (hello, headcount reconciliation) to just about anything your manager asks you to do because of HIS deadline, not yours.

Important + Not urgent

In my opinion, the box that is most important is the top-right.  These are the tasks, action items or projects that you will place there at the time of inception or at that light-bulb moment.  Really awesome task managers will have more items in this box than in other boxes and keep it that way.  The goal is to make sure the items here are killed before they become urgent, hence, spill over to the top-left.  Get it?

Not important + Not urgent

The last one, bottom-right, has a special place in my heart because most of the tasks that end up here have a way of killing itself off.  That is the way it should be because if they are not important and not urgent, in a few days or even hours they are probably not worth working on it after all.

Try it. You can use a white board, a notepad, or a Word document - It is so simple you'll probably even have fun doing it.