I particularly wear one all the time.
The Miraculous Medal was created in response to a request from the Blessed Virgin Mary, who entrusted us with our mission. It was given by the Blessed Virgin Mary herself! No wonder, then, that it gives such extraordinary graces to those who wear it and pray for Mary’s intercession and help. Our Lady manifested the Medal to St. Catherine Labouré on November 27, 1830, in the motherhouse of the Daughters of Charity of St. Vincent de Paul and St. Louise de Marillac, in Paris.
It is also good to pray Novenas from time to time, here is one Miraculous Medal Novena version: