The best thing that stills my mind is concentrating on work (which could be linked to Csíkszentmihályi's flow state) or doing meditation. There are many different states of mind meditation can help induce and maintain. I think the basic categorisation splits meditation into two types: (a) concentrative/active and (b) receptive/passive. The fastest and most efficient technique I found is the Wim Hof breathing technique: https://youtu.be/tybOi4hjZFQ