There is no simple way to determine the products of an arbitrary chemical reaction. There are some general rules to memorize, and some typical classical experiments to use, but its going to be difficult, not matter what. And I just wanted to be sure you knew that.
Now, the thermal decomposition of NaHCO3 is actually pretty well known, and many references should exist for the reaction. If you really want to figure it out for yourself -- can you try to guess what products are possible? Its a good way to learn, even if you guess wrong at first.