Does God care about how we worship him when we are gathered as his people? 
Now Nadab and Abihu, the sons of Aaron, each took his censer and put fire in it and laid incense on it and offered unauthorized fire before the Lord, which he had not commanded them. And fire came out from before the Lord and consumed them, and they died before the Lord. (Lev. 10:1–2)It seems rather hard to conclude that Israel was free to make up her gathered worship as she went along. If Israel was weak and unable to determine how to worship God aright, what makes us any better? If God gave Israel principles and commands concerning gathered worship, has he not also given us such principles and commands?
But when [Uzziah] was strong, he grew proud, to his destruction. For he was unfaithful to the Lord his God and entered the temple of the Lord to burn incense on the altar of incense. But Azariah the priest went in after him, with eighty priests of the Lord who were men of valor, and they withstood King Uzziah and said to him, “It is not for you, Uzziah, to burn incense to the Lord, but for the priests, the sons of Aaron, who are consecrated to burn incense. Go out of the sanctuary, for you have done wrong, and it will bring you no honor from the Lord God.” Then Uzziah was angry. Now he had a censer in his hand to burn incense, and when he became angry with the priests, leprosy broke out on his forehead in the presence of the priests in the house of the Lord, by the altar of incense. And Azariah the chief priest and all the priests looked at him, and behold, he was leprous in his forehead! And they rushed him out quickly, and he himself hurried to go out, because the Lord had struck him. And King Uzziah was a leper to the day of his death, and being a leper lived in a separate house, for he was excluded from the house of the Lord. And Jotham his son was over the king's household, governing the people of the land. (2 Chron. 26:16–21)
Everything that I command you, you shall be careful to do. You shall not add to it or take from it. (Deut. 12:32)
Of course, some of those principles carry over from worship under the former administration, but we have to be careful. For example, Christ's one sacrifice has rendered any attempt to offer a further atoning sacrifice blasphemous; but we do seek forgiveness on the basis of God's promise just as Israel did.
So what principles are there which we find? From the Old Testament, there is the seeking of forgiveness and the offering of support to the work of the church. The mere existence of the book of Psalms, as well as our knowledge of its use, tells us that corporate singing is to be expected in our gatherings, and Paul repeats this in the New Testament. Ezra sat down and taught the people from the Law of God, and we ought to be taught from God's word today, being devoted to the apostles' teaching. Clearly this requires the public reading of Scripture. Apart from the apostles' teaching and the concomitant reading of Scripture, Luke also mentions the fellowship, which may be supported in the offerings as well as the ritual consumption of Coffee and Biscuits; the breaking of bread, which we may take as a synecdoche for the sacraments; and prayer, which is obvious enough and also comes from the Old Testament worship. This pretty much covers the range of things we put in our services; but given that all things must be in order, how do we structure them?
Well, the Bible doesn't lay down a specific order, of course, so we are free to vary it as appropriate, but there are some general principles which ought to inform our structuring, and these flow from an understanding of what the church is, with regard to the Gospel. The church, you see, is the people God has gathered by his word. Thus, our gatherings occur by the calling of God, and we respond. The structure may seem dialogical, but it is always God who speaks first. In what follows, I'll give a model order, which isn't to be followed slavishly but rather demonstrate that there are things which are moveable (notably, songs and prayers, and to an extent, Scripture readings) and things which must be fixed.
It is right, therefore, to open the service with a call to worship from Scripture. And having been called, we respond, in song or perhaps in prayer. What then?
Before we reach the word of God's grace, we must hear his Law. Therefore, it is proper that the Law be read: either the Ten Commandments, or else the Lord's summary of the Law. The only proper response to God's Law is to confess our sin and manifold wickedness; and God's promised response, which all Christ's servants have the authority to proclaim, is forgiveness. We respond in song, perhaps, and more fittingly after a confession of sin, a confession of faith. The content for this is customary, but of course, the Bible doesn't require us to use an ecumenical creed. You may argue that the Bible doesn't require us to confess our faith. I would counter that this is an elaborate "Amen" to God's word of forgiveness: we believe that you forgive us, God, because we believe you have shown yourself to be this God.
If there is only one Scripture reading, then it is appropriate to place it here; if there is more than one, they may need to be distributed somewhat more widely. Having come from a tradition in which "This is the word of the Lord: thanks be to God" was not a common feature of worship, although the front-led "May God bless the reading of his word today" was, I've come to understand and appreciate the reasoning behind that particular response to God's word. That, or something similar, is good to use, to involve the congregation in an immediate response to God's word. Then we respond more fully, perhaps in song, and certainly (because they must go somewhere…) in prayers on intercession.
And then we reach the sermon. Oh, this is the fun one. If the sermon is declaring God's word to us, then it must be declaring the Law in all its sharpness and the Gospel in all its sweetness, surely. And having so heard God's gospel once again, we respond with offerings of thanksgiving and song.
If Communion is celebrated, then we continue through the dialogical structure: God calls us to his table, we respond in song and prayer, Christ tells us that before us are set his body and blood and then feeds us, and then we sing or pray in thanksgiving.
Finally, God blesses us as we depart. Wot, no response? you ask.
We respond by living lives of thankful service throughout the week.
 If I use the word "worship" loosely here, I am referring to our gathered worship as the people of God, and not to worship in the sense of the whole life lived. This, certainly, is our spiritual act of worship and the spiritual sacrifice acceptable to God through Jesus Christ (Rom. 12:2, 1 Pet. 2:5). And as you will see, what we do on Monday is firmly linked to what happens on Sunday.