After you have your blocks drawn out, its time to emboss the blocks into the foam core. I used a wooden stylus, it is for sculpting with clay, I think I got it at Michaels. Any tool with a blunt tip will work.
You don't want the tool to be sharp because you do not want to puncture the outer paper of the foam core (notice I did in the bottom left corner below). A ball point pen will work well too. Take your stylus and rub back and forth over your lines to make a indentation in the paper of the foam core. Make it as deep as you can without puncturing the paper.
Then round all the corners of your bricks
Add some character - put as much or as little detail into it as you like.
"It ain't about how hard you hit, but how hard you can get hit, how much you can take and keep moving forward - thats how winning is done!" Rocky Balboa