There is a well-known and simple theory for betting the NBA Playoffs called the zig-zag theory. The zig-zag theory is simply to take the opposite of what happened in the previous game. For example, if the favorite covered in Game 1, then the theory would say to take the underdog to cover in Game 2.
While the theory had some early success, the more bettors that jumped on the bandwagon, the more books shaded their lines to counter this betting system. Even though the theory is 2-0 in the NBA Finals, (although some bettors will start the system over when the series moves to a different city) the system has faltered in the long run.