I've always found that counting the breath works really well to improve your focus. As you exhale, say the number "one" silently, then with the next exhale say "two" etc. Make sure you say the number for the entire breath and try to let the number fill your mind. When you lose track of which number you're on, go back to one. However, if you have a thought but don't loose track of the sequence, just let the leave with the breath and continue. You may not get passed the number two before you have to start again, but don't worry--it will come. This is also a great thing to do whenever--you don't need to be sitting on a cushion.

Good luck,

Chris
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"Seek not to follow in the footsteps of the men of old; seek what they sought."
--Basho