Some people find that as soon as they open a book for serious study, intrusive thoughts creep in which disturb concentration. These may be memories of the past, worries about the future, recent quarrels and arguments.
Therefore, difficulty in concentration does not stem from a lack of thinking ability, but rather as a result of the power of one's imagination. By calmly pushing away those extraneous thoughts, you will be able to achieve greater concentrate on the task at hand.
Today, before you begin a certain task, try verbalizing your intentions. Telling yourself aloud how you want to apply your mind for a certain period of time often works to block out extraneous thoughts.
(see Alai Shur, vol.1, p.24; Rabbi Noah Weinberg's 48 Ways to Wisdom; Gateway to Happiness, p.84)