A lot of churches have a live band play a set of 2-5 songs at the start of a service to set the tone. It serves the purpose of focusing the congregation in on God. Being a player in a church band requires a little more flexibility than your usual covers band. In that the format of the songs isn't as locked down as you'd like. The lead singer (worship leader) is often given the ability to re-arrange and re-interpret the song on the fly.
Also you are often dealing with a much wider range of skill levels than in a traditional band, as all (most?) the people on stage, and behind the mixing desk are volunteers. So you get professionals with 20 years of stage experience playing next to someone that knows 5 chords and doesn't own a tuner yet. In terms of music it's fairly pop/mainstream as that appeals to a wide audience. The use of delays and chimey guitar sounds is very prevalent. Although finally some non-trival use of synths and keyboards is appearing in the last few years.
Sometimes the band will segue into a "free worship" section of a song, which is usually dynamic and improvised at a melody and lyrics level. The main thing however is just being sensitive to whats going on around you. e.g. if the previous song ended with a quiet tail and the next song has a hammer down intro... sometimes you have to come up with a way of starting that without going all in. Conversely sometimes things call for raised dynamics and leading out with a strong riff.
I find that unless you have a larger team with more than one electric, the guitar is going to be mostly rhythm. Ideally lead parts are keep to well defined sections.
My $.02
PS dunno about other churches but we often have to play any given song in a variety of keys. Keeps you on your toes :-|
