In the medium term, the best contribution that monetary policy can bring to economic performance is to maintain a low and stable inflation rate and to have very clear expectations in this respect. In the medium and long term, this is the best thing to do.
Of course, the short term inflation rate is very much influenced by pressures on the economy, either upward or downward. When there are upward pressures, when the economy is working at a level higher than its potential, there is inflationist pressure. This is when monetary policy must be tightened up.
On the other hand, when there is a great deal of slack in the economy and pressures to bring inflation down then we must exercise more expansionist pressures on monetary policy, but...