There are other things, however, which are different in different places and countries [...] In regard to these and all other variable observances which may be met anywhere, one is at liberty to comply with them or not as he chooses; and there is no better rule for the wise and serious Christian in this matter, than to conform to the practice which he finds prevailing in the Church to which it may be his lot to come. For such a custom, if it is clearly not contrary to the faith nor to sound morality, is to be held as a thing indifferent, and ought to be observed for the sake of fellowship with those among whom we live. Augustine, Book I of Replies to Questions of Januarius, Par 2.
This is a counter-intuitive teaching. One would think that it would be more important to give God the highest form of worship, regardless of what others are doing, than to fit in with everyone else. St. Augustine does not seem to be of this opinion, however. In fact, he followed this passage immediately with the example that a person ought not to fast on Saturdays when in a community whose custom is not to fast on Saturdays. To fast is good by its very nature. Voluntarily accepting hunger in order to be more wholly detached from worldly pleasures and more totally given to God will bring us closer to God. This counter-intuitive teaching is driven further by Augustine in Par 5, in which he speaks against the condemnation of one place’s custom as a response to finding an apparently better practice elsewhere, saying that such condemnation "would show a childish weakness of judgment against which we should guard ourselves, and which we must bear with in others, but correct in all who are under our influence."
Although this clearly does mean that whether we follow a custom should chiefly be determined by what the community is doing, this is not a license to relativism. One practice may very well be better than another, but it is more important that we are humbly united in Christ under our bishops than that our customs are perfect. St. Augustine is not saying that no custom is better than another, but is saying that it is more important for a community to be united in a good worship than it is for an individual to perform the best worship. St. Augustine very clearly viewed acceptance of a custom by the universal Church to be authoritative proof that it is good (pars. 1, 5, 6, 8), going so far as to say, "If the universal Church follows any one of these methods, there is no room for doubt as to our duty; for it would be the height of arrogant madness to discuss whether or not we should comply with it." (Par 6)
We can learn from St. Augustine our proper place as the laity in regards to disciplines of the Church. We ought to abide by local customs, even when another custom may be better, for the sake of unity. Acceptance by the universal Church authoritatively proves a custom to be good, to such an extent that St. Augustine referred to mere discussion of whether we ought to comply with it as "the height of arrogant madness". We ought to accept the disciplines of the Church then with docile humility, only going beyond the customs when doing so would not be disruptive.