The first thing is to look. Regardless of the variety, melons with clear skin lines, bright color, concave pedicles and navels, and thick vine roots are considered good melons. The second is touch. A good melon has a smooth skin and a firm feel. The third is weighing. Ripe watermelons are relatively light. For watermelons of the same variety and similar size, the lighter the better. Finally there is the bomb. Hold the watermelon in your hands and tap it gently with your fingers. It will make a crisp sound of "dong, dong" and the hands of the watermelon will feel trembling. If the watermelon makes a muffled "pop" sound and feels soft to the touch, it is usually overripe.