I do not know for sure when I began praying daily for our government leaders. My best guess is about 1985, when Ronald Reagan was president.
About that time, my prayer life was radically altered by attending a prayer conference led by Don Miller at Ellisville Baptist Church in St. Louis. At that time, private devotional time became a permanent fixture in my life.
I have prayed for presidents I agreed with, and ones I disagreed with. I have prayed for God's wisdom for them, and for God to use them for His honor and glory.
I also pray for other government leaders, especially those I have served as Pastor and/or personally known. On a side note, I find having a picture of the official to pray over to be very helpful.