Here's a wonderful tour de force on Concentration that's written for students and which includes tips on identifying distractions as well as a useful list of techniques for putting your attention where you want it to be and keeping it there.

A few I liked:

• At the beginning of a study period, spend a few minutes to calm and relax your mind and body. (Try 'Focus on Your Breath' exercise, below.)...
• Do not tell yourself off or tell yourself to concentrate. When you are thinking about not concentrating, you are not concentrating....
• If you find yourself feeling overwhelmed by all the things you have to do in your life, remember that you can only do one thing at a time...

We have lots more here on battling distraction, including this excellent essay on "good" distractions by Paul Ford.