What's the quickest way to clear my mind?

Exercise: Exercise is a great way to forget all your worries for a brief period of time and decrease your stress levels even afterwards. Try yoga for body and mind!

Mindfulness: There may not be a quick way but there is an effective method called mindfulness which is a meditation technique. There are books and therapists who teach it. Briefly, it involves focusing on your breathing and letting thoughts enter and flow out of consciousness. Treating thoughts as if they are leaves floating down a stream, first entering awareness and then letting them go.