They developed a rules-based approach to the conduct of monetary and fiscal policy and published it in 1990 in the Economic Report of the President. That essay laid the foundation for what is perhaps John's most well-known contribution to economics--the simple description of the determinants of monetary policy that eventually became known as the Taylor rule.
1 John's analysis triggered an avalanche of studies examining the stabilization properties of Taylor rules in the context of macroeconomic models. Other work investigated the ability of variants of the Taylor rule to describe empirically the actual course of monetary policy in the United States and in other economies.