First I find a square ruler or template (I collect the things) that is larger than the figure that I want to fussy cut. Then I figure out the size that the block needs to be (remember that you will be sewing in 1/4" from the edge on each side). When I have a good idea of the size, I take a marking pen and outline the piece and then overcut around it with scissors. Then I cut it out using the rotary cutter on the drawn lines.
Hoe this helps.