There are a couple of ways of doing it, playing chess helps.
Without giving you every step notation form I'll try and describe the start.
Always try and move around the grid in a clockwise position by taking the block that is nearest the edge of the grid.
If you get to a choice of blocks and the block nearest the edge means you have to go counter clockwise for that block then you must take that one but then immediately take the next clockwise one again and continue on clockwise until a similar scenarion occurs.
Eventually you will reach a position where you will have an almost solid square of untouched blocks left in the midle of the grid - you're on your own from here
