The key to a good steam boat is the soup base. There are many ways to prepare the soup base. A common way is to use pre-made chicken stock from the supermarket and add vegetables in it to provide the sweet taste.
There is an easy way to make a good spicy soup base using Tom Yum Soup Paste (if you don't eat chilli food, then it is just too bad). Add a few table spoons full of paste to boiling water and off you go!
According to my friends, the Namjai brand is the only one that will give you the kick, so make sure you get the right one. Once the soup base is sorted, you can put whatever you fancy in it. Normally people put fresh meat, fresh vegetable and even fresh oysters.
But if fresh oysters are too hard to get or too expensive, frozen oysters are as good. In fact, I found that frozen oysters are even better for steam boat. By the time they are cooked in the pot, the centre of the oysters are only slightly cooked, therefore the texture and sweetness of the oysters stay.