Hadith: The Messenger of Allah (may Allah's peace and blessings be upon him) preferred beginning with the right side when wearing his sandals, combing his hair, purifying himself, and in all his affairs.

عن عائشة رضي الله عنها قالت: «كان رسول الله صلى الله عليه وسلم يعجبه التيمُّن في تَنَعُّلِّه، وترجُّلِه، وطُهُورِه، وفي شَأنه كُلِّه».
[صحيح] - [متفق عليه]

‘Ā’ishah (may Allah be pleased with her) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) preferred beginning with the right side when wearing his sandals, combing his hair, purifying himself, and in all his affairs.
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

‘Ā’ishah (may Allah be pleased with her) informs us of a beloved habit of the Prophet (may Allah's peace and blessings be upon him) which was beginning with the right side when wearing his sandals, combing and fixing his hair, cleaning himself from impurities, and in all similar affairs, like wearing long shirts and pants, sleeping, eating, drinking, and so on. This was done out of optimism as well as honoring the right over the left. As for dealing with unclean things, it is better to start with the left side. That is why the Prophet (may Allah's peace and blessings be upon him) forbade using the right hand in cleaning oneself after answering the call of nature, as well as touching the penis with the right hand, because the right hand is to be used in doing all good and pure things, while the left hand is to be used in things other than that.