It is mentioned in Mirqaat that this when one is ascending the stairs of his house or Masjid, then he should begin with his right foot and say Allahu Akbar, even though it is only one stair. At the time of descending, begin with the left leg and recite ‘Subhaanallah’ although it is only a small decline.

There is hope that one will recieve the reward of practising on a Sunnah. Mulla Ali Qari RA has mentioned the wisdom in saying at the time of ascension, that although apperently we are going higher but O Allah! we are not high. Highness and greatness are only for you. While descending, a person because we are low and O Allah! You are free from lowness.