While some would greatly expand and others may somewhat reduce the following characteristics, in general a Reformed local church has these several prominent features:
A Reformed Church Emphasizes the Means of Grace
The means of grace are the God-appointed ways that his saving and sanctifying grace comes to us. They are found in Acts 2:42: "And the disciples devoted themselves to the apostles' teaching and the fellowship, to the breaking of bread and the prayers." These means of grace might be called the raw elements of corporate worship.
The Reformers defined the church as the place where the word of God is rightly preached and the sacraments rightly administered. God's transforming grace clusters about these elements of worship. Reformed churches not only prioritize the biblical means of grace, they conform their public worship exclusively to them. Preaching is central in Reformed churches and flanked by the Lord's Supper, baptism, and public prayer.
A Reformed Church Emphasizes Preaching the Most
The pulpit in a Reformed church is placed front and center, for the preaching of God's word is the chief means of grace. God's creative voice goes forth in the opening of his word to his people by the living preacher. Books are good and studies are helpful, but it is in the formal, Lord's Day, public exposition of the Bible that God speaks most clearly to us.
In fact, preaching is so central to Reformed churches that they believe the preaching of the word of God is the word of God. In other words, the live preaching of God's word is not commentary upon the text but unleashing of the text upon the hearts of present hearers. The Bible was designed by God to be cut by faithful, called expositors who bring the text to bear on his people every Lord's Day. And it is there, at the sacred desk, that we hear God remind us week in and week out that our salvation is by grace alone through faith alone in Christ alone to the glory of God alone.
More may be added but in my estimation, these are the marrow elements of Reformed assemblies. If I added anything it would be that Reformed churches are confessional: they hold to a confessional standard of one sort of another (Westminster Standards, Savoy Declaration, 1689 Second London Baptist Confession). Here I have lighted more so upon what a Reformed church looks like.