Our green grocer told me how to pick a ripe honeydew and his advice has been right on the spot. Feel the skin of the melon and if it has a sticky feel to it it's ripe. This means that the melon has ripened to the point that the sugars in the melon are extruding through the skin surface. Hope that helps. Also doesn't hurt to wait until the vine drops off the melon, but you should be able to pick it anytime it starts to feel sticky.