List all of your tasks—even ones that aren't bugging you right now. Leave room on the left for three columns labeled U, I and P. I'll explain these next.
Rate the Urgency (U) of each task. Do not be concerned with how important it is. This only takes into consideration that you will be penalized in life (money, grades, health, inconvenience, losing your job, etc.) if you are late doing these things.
For example, studying hard for your chemistry test may not be important because it'll be pretty easy and you already know the stuff, but it is urgent, because the test is later this afternoon and if you don't review, you'll not get the best grade you can.
Checking Facebook is urgent but not important.
Rate each task for urgency on a scale of 1-3 or 1-5 or whatever makes sense to you.
Rate the Importance (I) of each task. Do not be concerned with how urgent it is. These are the things that you must at all costs, but ignore whether it has to be done now or later.
For example, if you don't pay bills, your life will change dramatically for the worse, but maybe nothing is due until next month. Paying bills is very important but may not be urgent.
Calling your mother is important, but not urgent.
Rate each task for importance on a scale of 1-3 or 1-5 or whatever makes sense to you.
It's important that you do not fill in both U and I columns for each task at the same time. If you did, go back and erase them and do all of the U's then all of the I's, otherwise you'll skew your own results by superimposing your belief of priority, rather than letting the system work.
Now, go down and multiply each U and I together on each task. Put this number in P. This is your Priority.
Sort by priority, and sub-sort by urgency.
For me, when I do this, something magical happens—I say “of course” and figuratively slap my forehead—the tasks are now prioritized exactly the way I “knew” they should have been all along.
Select your top priority task and use the Pomodoro Technique. Work for 25 minutes, rest for 5 minutes. Hell, promise yourself you'll only spend 25 minutes and quit if you are not getting anywhere. Sometimes I don't know where to start. I just tell myself “just spend 25 minutes researching how to begin.” I generally find that when the timer rings (I have a Pomodoro iPhone app) I'm already halfway done with the whole project.
And cross things off as you complete them! It makes you feel so good!
Remember: Getting started is half the battle.