To choose a good watermelon, look for evenly sized, large melons with no cracks or pitting. They should smell fragrant, and the stem end should be indented. They won't ripen after they're picked, so if you end up with a dud, hit it with a small sprinkling of salt (large-crystal sea salt is great for this) to brighten the flavors and add crunch. Salt it right before you plan on eating it; too soon will detract from the moisture. -- Food Network Kitchens