This is the 7442nd most frequent Chinese word.
行之
"行之" means "to put into practice" or "to carry out."
In this sentence, '行之' means 'to practice or implement'. It indicates that the rule has been put into practice for a significant period of time.
这个规则已经行之多年，效果非常明显。
This rule has been practiced for years, showing substantial results.
Here, '行之有效' is a set phrase meaning 'effective in practice'. It suggests that the measure is proven to work.
他对这个计划表示认可，并认为行之有效。
He expressed approval for this plan and believed it to be effective in practice.
The phrase '行之有序' entails doing or carrying out something in an orderly manner. '行之' here refers to the act of implementing or putting into action.