This quote comes from Chapter 11 and is set at the New Year's party where Godfrey Cass and Nancy are the subject of fierce speculation regarding their relationship. What is important to note is that this quote comes as Eliot shifts the perspective from her normal authorial, omniscient narrator stance and moves it towards the thoughts and feelings of the common folk who are fortunate enough to be present at this august event. Eliot continues this quote by saying that the sight of some of the senior members of Raveloe dancing together at this party "renewed" the charter of Raveloe. Her explanation of this is important in order to help understand this quote:
It was not thought of as an unbecoming levity for the old and middle-aged people to dance a little before sitting down to cards, but rather as part of their social duties.
The quote in this question therefore relates to how the Squire and Mrs. Crackenthorp and other important pillars of Raveloe society fulfilled their social duties by leading the way in dancing on this joyful social occasion. The indication that this was what "everybody was used to" shows that Raveloe is a village built on tradition, and this is very important to the sense of identity of this village.