Step 1: Buy a watermelon. Step 2: First remove the top and bottom of the watermelon with a large chef's or serrated knife. Step 3: Halve the watermelon with a vertical slice. Step 4: Following the curve of the fruit, cut the skin off in vertical slices. Step 5: Cut the watermelon crosswise into slabs. Step 6: Turn the slabs so they are laying flat on the cutting board. Step 7: Working on one or two slabs at a time, cut into long pieces and then into slices or cubes.