It’s just strumming the chords isn't it?
The acoustic guitar can carry a congregation without the need for other instruments at all, but in a group setting its main job will mostly be add movement and some ‘body’ or 'sparkle' to the sound. Probably best to only have one acoustic guitar playing at a time, and let the rhythm section do the hard work! By which I mean that strumming lightly, cleanly and in time will be better than thrashing the strings which tends to give a very scratchy sound.
Often if there’s a band playing with you, it may be appropriate to strum just once or twice per bar, rather than feeling that you need to drive the rhythm. This gives more space for the other instruments to work in, and can help with dynamics so that you can build up to full strumming for certain sections of the song. For a lighter sound, it can be effective not to include the lowest couple of strings when you strum.
Finger picking is often a great option for gentler songs because it gives movement and rhythm but in a very mellow way.
Am I in tune?
Good question! Few things are less pleasant to listen to that a guitar that's out of tune with itself or other instruments. Tuning is really important for guitarists and although it can be a distraction if you keep stopping to tune up during a worship time, there is a lot to be said for checking it regularly. An electronic tuner that you can plug into (if your guitar has an audio output socket), or hold near the guitar will generally be more accurate than trying to do it by ear, especially in a noisy environment.
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Are capos good or bad?
A capo is obviously useful for transposing so that you can play easy chords in a difficult key. But why not take the time to learn some of the trickier chords and don’t rely on the capo to do the complex stuff!
However a capo is an excellent tool if you want to actually change the sound of the guitar. By moving it up the neck you are effectively shortening the strings so that chords will sound different. This can be a great way of moving the guitar sound into a different register and out of the way of other instruments (such as the electric guitar) that might be occupying that octave. This can open up the sound and make it easier to hear each instrument working in its own space.