Sentence:  Here's a way to start improving your balance right now. Let's tune into a reference point, the place on which you can feel your weight concentrated, the spot that will always let you know whether or not you are in balance. I call this reference point the "<WSD>sweet spot</WSD>" of your foot. The <WSD>sweet spot</WSD> is just behind the big toe and to the side of the ball of each foot (some people grow bunions on this point). 
Meaning of the word marked with <WSD> tags:  Any place that is optimal for obtaining a certain desirable effect or result.