Whether you are a beginner, or coming back to playing after a long period of time, it is important for you to feel comfortable playing on your own, before you attempt to play with or in front of others.
Learn and practice the main chords, until you are able to move between them quickly and without looking at what your fingers are doing. It may be wise to invest in a guitar chord book, or some lessons from someone already an accomplished guitarist.
Learn the sequence of chords for some of the most popular Church songs. As a regular Church-goer, you should know the songs sung by the congregation. You can get a copy of the song chord chart from the Internet.
Keep up-to-date with new songs being released. This will help keep the Church worship fresh and inspirational. You can easily check this out on the Christian Music websites, or in your local Christian bookstore.
Play with others in the Church. Playing as part of a Worship Team is great for building your confidence, and learning how to play in a band. This will also help you to know the Church's arrangements for each of the songs they do.
Once you have worked out the song arrangements, and how you want to sing and play them, you may be ready to play in front of others. If you attend a house group, this may be a safe environment to start off.
Work out with the group leader how many songs you may play at the performance, and if they will sing with you so there are no surprises. Confirm whether you will play at the beginning, the end, or both.
Spend time in prayer. Before you can lead others (even if you are part of a team rather than the worship leader) in worship or praise, you need to be in that place yourself. This will help you to feel a peace about playing.
Work out the arrangement you want to play between each song; will you strum or finger-pick? Will you read a verse of Scripture or pray as you play? Be comfortable with what you are doing.
Arrive early and fully prepared. Pack your chord charts, guitar, plectrum and strap well in advance, so you are not left fumbling around before you are due to play. Then pray and relax. Have fun as you play your guitar with other believers.