Cut the stem ends off the watermelon. 

Carefully cut the watermelon in half. I start in one spot and slowly roll the watermelon all the way around, little by little, cutting more as I go. (see photos above)

Once a ring is cut all the way around, cut the rest of the way through the center, splitting the watermelon in half.

Lay one of the halves on the cutting board, with the middle flesh-y side down. 

Start to peel away the rind with your knife, one section at a time from top to bottom, while trying to preserve as much watermelon flesh as possible.

After the peeling is all gone, flip it on its side and make several large slices. (see photos above)

Then flip the stack of slices back on the flat side. From there, make long slices. This will create long spears, and you can leave them this way if you like. (see photos above)

To make cubes, rotate the watermelon (still on its flat side) ninety degrees, and make cubes. Just like a checkerboard! (see photos above)

You can use your knife to scoop the chunks into a serving dish or storage container. Refrigerate anything you don't eat for up to a week.