There are several methods to develop one's concentration. One of them is very simple: eat a segment of an orange in 5 minutes. This is not as easy as it sounds. 5 minutes are pretty long for that. :)
The exercise is done properly if you pay attention to the color, texture, smell, taste, etc. of the orange, so you don't just put it into your mouth and swallow it, but pay attention to the whole experience.
I tried it several times, but I always failed. I didn't manage to hold out for 5 minutes. It seems either I can't concentrate properly or I'm simply a glutton. :D