That's why we advise that people practice meditation. Work your way up until you can focus on a single word/image/thought for 20-30min. Start small, 2-5min a day, then when you're good with that, add a few more minutes until you have to actually stop yourself consciously, not that your mind interrupts.
Unfortunately, this is one of those problems that just takes practice and concentration work. And indeen, meditation is the key here.
I call these kind of meditation concentration meditation. These are probably the most common and well know of all the meditations and often meditation is defined by these kinds of meditations exclusively. They are closely related to the Insight Meditation Techniques, with the difference being that Insight Meditation Techniques utilize the active application of intelligence and discernment, while the Concentration Meditation techniques use the power of focused attention to a greater degree. To some extent these meditations lay the groundwork for the Insight Meditations which need a high degree of concentration as a prerequisite to being effective.
Look at google and search for articles about methods of such meditation, you'll see that it is covered very well.