It's as easy as 1, 2, 3! 1  Look the watermelon over. You are looking for a firm, symmetrical watermelon that is free from bruises, cuts or dents. 2  Lift it up. The watermelon should be heavy for it's size. 3  Turn it over. The underside of the watermelon should have a creamy yellow spot from where it sat on the ground and ripened in the sun.