As stated in this passage from the Pali Canon ( Samyutta Nikaya's Kaccāyanagotta Sutta):
"'Everything exists': That is one extreme.
'Everything doesn't exist': That is a second extreme.
Avoiding these two extremes,
the Tathagata teaches the Dhamma via the middle...."
In everyday life situations, this can be practiced through the perspective you use to watch events unfold. It is a state of awareness that can sound paradoxical when described. It's like looking in opposite directions at once. You give attention to your surroundings and present situations, yet simultaneously stay focused on how you feel and the thought processes (or lack there of) going on. In other words, you are looking out and looking in.
This perspective slows the mind. Whenever we give our attention to our mind and/or our breathing, they will slow down. Our awareness is present like always but we watch the amount of thoughts passing slow down. Of course this attention can only be given in the present moment and aligns your awareness with the present moment. In this frame of consciousness, extremes fall away.
Extremes are resorted to in stressful situations. Ego threatened thought produces stress. When a person slows or eliminates excessive thoughts, they can effectively slow or eliminate stress. No stress...no extremes. The middle road. The middle way.