Often a curious person may ask themselves this very question when thinking about going to church. Sometimes they may take it a step further and ask their friends or visiting some websites to read up or dip their toes in the water before diving in and attending a service. One of the difficulties for people answering this question is that what someone is told they ought to expect and what they may find are often quite different.
The idea of having expectations implies a standard or some authority. It is completely proper for a first time attendee to expect the church they visit to conduct things decently and in order (1 Corinthians 14:40). It is also good for a visitor to expect to find the church's worship to conform to the teaching of the New Testament on worship. Jesus said that true worship is in spirit and in truth (John 4:24). This means that it is done with the correct attitude and the correct standard. An Old Testament character named Joshua used a similar phrase calling on the old nation of Israel to serve God in sincerity and truth (Joshua 24:14). Another statement Jesus made explains what it means to worship in truth when He said to the Father, "Sanctify them through thy truth: thy word is truth" (John 17:17). Worshipping God is only true worship when it is with the proper attitude in sincerity and with the proper authority according to God's word.
When you show up to a church building there is no standard given in God's word to regulate what it ought to look like. Some buildings are beautiful stone structures; others may be built like a house while other churches meet in offices or storefronts. Some places of worship may have a steeple while others may not; some may have stained glass and others may not. Worshipping in spirit means that the worshipper carries the reverence in their heart and it is not dependent upon the carpet or woodwork. There are all kinds of options which are not really the most important thing when it comes to selecting a place to worship. The church is not the building, but the people (Acts 15:3; Acts 2:47; Romans 16:3-5).
When you arrive at a place of worship and begin to meet the people some may be boisterously friendly and others may be quiet and timid, this is because, like you, they are people and a church has a diversity of personalities. The important thing is that they are all trying to become more like Christ and use their particular talents and personalities to the greatest in the Lord's service. Many people are afraid that they will be judged, ridiculed or spurned when they come to church and the truth is that most churches are really enthused to see visitors.
Often people also worry about what will take place or what they are supposed to do when they attend. Some churches offer a Bible class before worship which is for the study of the Bible or Bible topics. Visitors are invited to these as well before the service. It may seem difficult or odd coming into an unfamiliar class in the middle of the study, but don't be discouraged, it's normal and the feelings will change as one continues to attend. Some offer the classes before a worship service and others after while some churches do not have such classes on Sundays. Some churches use the time when everyone is together to give announcements on things that relate to the whole congregation, but this is a choice and varies between churches. In the worship service itself there are some essential things a visitor ought to expect.
First, they can expect to see and hear the church engaging in singing. This singing is an act of worship. Singing offers praise to God and also by so doing the church teaches and admonishes one another (Colossians 3:16; Hebrews 2:12). Visitors may be surprised when they don't see a band, an organ, a piano player, or even a choir performing to or with the assembly. The reason for this is that God gave the command to sing; a command for each individual to engage in worship. The mechanical instruments offering their sounds to God would be an addition to the simplicity of worship God commanded under the New Testament (Colossians 3:16-17; Ephesians 5:19; Leviticus 10:1-2).
Secondly, visitors should expect to see the church praying together to God. Christians pray to the Father through Jesus Christ (Matthew 6:9; John 16:23; 26).The church ought to pray together and they may have several prayers throughout the service (1 Timothy 2:8, Acts 2:42; 1 Thessalonians 5:17). These prayers may range in their content from praise to God, thankfulness for blessings both spiritual and material, the providence of God for things generally or specifically for special needs of the congregation.
Thirdly, a visitor should expect to see the congregation taking the Lord's Supper (also called communion) each Sunday in its worship service. This was the practice of the early church described in the Bible (Acts 20:7; Acts 2:42). The Lord's supper service is a simple ceremonial meal where one eats unleavened bread and drinks fruit of the vine (i.e. grape juice) as they contemplate the body and blood of the Lord Jesus Christ in His death. This memorial reminds the worshipper of the sacrifice necessary to atone for sins and the reality of Christ's death (Matthew 26:26-29). Partaking of the Lord's supper is a communion with Christ and with one's brothers and sisters in Christ (1 Corinthians 10:16).
Fourthly, the congregation as a whole will engage in hearing God’s word. This usually comes in the form of a sermon. The apostles and teachers in the New Testament delivered sermons in the worship services (Acts 20:7; Acts 2:42). The preacher is just a leader in this act of worship just like a prayer leader leads the congregation in prayer and the song leader leads the congregation in singing. Preaching is the method of making the church strong and pure (2 Timothy 4:1-2; Acts 20:25-32). The sermon may be over biblical teaching on some matter of church doctrine, moral living, or a current event and is largely at the discretion of the preacher or the eldership, but a preacher must preach the word and not simply entertain with clever stories and quotes. A preacher should reprove, rebuke, and exhort all the while pointing to the way to salvation.
Finally, the congregation will take time in the service for giving. The contribution was a part of the worship where each worshipper gives as they have prospered for the work of the church (1 Cor. 16:1-2; 2 Cor. 9:7). Most churches take up this collection immediately before or after the Lord's supper, but it is a separate and distinct act of worship.
Many people worry about coming to service underdressed or overdressed. It's really not necessary to agonize over this. God cares about us being considerate more than the price or quality of our clothes. As a good rule of thumb, ask yourself how you would feel comfortable presenting yourself before the CEO of your company, the president, or God and both God and the church will be happy to see you visiting.