I worked horizontally, from the bottom up, but certainly could have worked in vertical strips, too. Because I was assembling several rows at once, I tried to label the left-most square of any row (using masking tape and a pen); I also tried to keep written track of which squares had been made and which squares had been joined.
More than once I got bogged down with the pattern, and I even had to tear out two rows when I discovered two errors.
The classic Jolly Roger has a pair of crossed bones below the skull, but I also found other designs, including swords, a single bone, words, and even a heart.
I am not finished with this project, but when I posted pictures of the work in progress, my cousin asked for the plan.