Step 4: Gluuuuuuuuuue!
Now that you have all your squares cut out, they may need a little flattening. Get a Lego guy to help you, or lay a big heavy book like the Bible or the Koran or The Stand on there. Once the pieces are flat enough for you, you'll want to arrange them on your posterboard and see how they will fit. I only had a strip of board, so I didn't do all the shapes. with a full sheet of posterboard, you could have a whole fridge of tetris!
Once you're satisfied with the layout, heat up your gluegun and get cracking!