Steaming is most suitable for root vegetables that will not be damaged by the longer cooking time. The vegetables should not come into contact with the boiling water, and to enable this you can buy wonderful expanding metal contraptions that fit inside your saucepans, or you can improvise with a colander. The saucepan must have a tightly fitting lid. You can also use those lidded wicker baskets on top of a saucepan, but make sure the water is boiling like crazy.
Here are a few vegetables suitable for steaming, and their cooking times: