How to pick a melon? First, choose one that feels heavy for its size. Second, for all melons except watermelons, smell them. Ripe melons smell like, well, melons!
Once you get that melon home, see How to Peel Melons and How to Slice Melons – both useful skills for making Melon Aqua Fresca or Melon Sorbet, perfect for cooling off in summer's heat. Or check out these 5 Quick Ways to Use Melons.