CO(g) + H2O(g) ⇄ CO2(g) + H2(g) + energy

Which change to the system would be favorable to the forward reaction?

Increasing the concentration of CO and H2O or decreasing the concentration of CO2 and H2 would be favorable to the forward reaction. Additionally, increasing the temperature or removing some of the products (CO2 and H2) as they are formed would also favor the forward reaction.