Do these exercises a few minutes a day. Don't demand to much from yourself in the beginning and increase the duration each day. I've just started doing these exercises and spends like ten minutes a day doing them.It really helped me in improving my concentration...
1. Close your eyes and start to visualize the number one in front of you and say "one" in your head when you see it clearly. Allow the one to disappear and start to visualize the number two and say "two" loud in your head when you see it. Repeat this procedure up to 100 if you can.
2. Choose a spot on the wall and look at it - don't focus too much on it though. Erase all thought from your mind and concentrate as hard as you can on your breathing. Hold on as long as you can.
3. Sit down and close your eyes. Clear your mind from all thought. Breath deeply and count each breath at each exhale. Hold your mind totally blank except for the counting as long as you can.
4. Select an object like a half eaten cookie, a coin, a pen - anything - try to relax every muscle in your body and concentrate on the object. Start thinking about its shape, color, material etc and try to memorize its form. Then close your eyes and try to visualize it in front of you. If you can't, open your eyes again and start over.
5. Write a dream log each morning when you remember a dream and every night before you go to sleep, review your day in reverse. This exercise will help you remember your dreams.