This is more of an exercise in practising concentration than it is in mindfulness.
In this exercise rather than focusing on your breath, you just close your eyes and focus your attention on slowly counting to ten. If the attention wanders off, simply bring yourself back and start counting again from one.
For many it goes something like this..
“One…two…three…do I need to buy milk today- ooops I am thinking.
One..two..three..four..this isn’t so hard- oops no.. that’s a thought
Keep going back to one until you can manage a count to ten without your thoughts wandering.
Source: Mindfulness Course, Tunbridge Wells, 2013