A ripe melon should give slightly when pressed gently at one end. For rockmelon, press at the stalk end. For honeydew, press at the end opposite the stalk. You should also sniff the melon: a ripe one has a strong scent and there will be little scent if it is unripe. A ripe watermelon sounds hollow when tapped. If buying by the slice, choose those that are bring red with shiny black seeds.
Freezing can dull the flavor of any melon, so adding a little lemon juice will help to sustain the melon flavor.
** Asian Recipes