Here are a few thoughts I have surrounding playing. Hope they're of use.

The Practical

• Don't just play the chords. A lot of the time that's fine, but think about whether you have to. Is there a way to play something a bit different rather than just marking the chords of a song?
  
  
• There are times to play loudly. We don't have small weedy God. Think of the noise coming from the trumpets as the Walls of Jericho fell.
  Psalm 95:1 Come, let us sing for joy to the LORD; let us shout aloud to the Rock of our salvation. 2 Let us come before him with thanksgiving and extol him with music and song...
  
  
• How many instruments do you play? It's at least two, guitar and silence. There's nothing wrong with not playing anything at certain points or even for a whole song.
  Psalm 46:10 "Be still, and know that I am God"
  
  
• Make a difference, don't just noodle around. Come in on the beat, have definite parts in mind that work with the song, think about exactly what you're going to play. If a song's on a CD have a listen to what's played on that for ideas.
  
  The title track from Matt Redman's ‘Blessed Be Your Name' live album is a great example of this, listen to the way the guitarists come in at certain points and how it makes the song feel.
  
  
• Keep it simple. Usually.
  
  
• With worship music it can be easy to become unsure of where things are going, will the worship leader repeat the chorus, are you heading to the bridge, the tag? Keep your ears open.
  
  
• Try to learn the chords and/or parts. It's not a problem to read the music as you play but it has drawbacks. You'll spend the whole time head down looking at a music stand which brings your attention away from listening and feeling what's going on. Moving between songs becomes harder as you have to swap music around. If the worship leader plays an unexpected song you'll be hunting for the music. Basically it's a distraction.
  
  I often have a few sheets knocking around for songs I'm not familiar with but I try to learn things as quickly as possible, generally by looking at the sheet a couple of times in rehearsal and then forcing myself to play without it.
  
  I'm still not great at this, but I find the more you do it the easier it gets. You'll also start to see the patterns in music, will begin to feel your way around musically and therefore spend more time thinking about how you play the song and not what the chords are. Playing along to a CD is also a good way to learn the chords/parts and to train your ear.
  
  
• Following on from above, for me the ideal when playing is that I have one sheet of paper. On it is a list of songs from the Worship Leader that we're probably going to play with the keys they're in and any short notes I've made in rehearsal.
  
  Generally those notes are about who's starting the song, any new or different structures that are tricky to remember and a few chords if I don't know the song or a particular part of it (like the bridge).
  
  

The Spiritual

• The environment you play in (size of building/congregation, location, church/secular venue, lights, sound, vision) should make little difference to worshiping.
  John 4:24 "...worship in spirit and truth".
  
  
• A lot flows from a personal private place of worship. I wish I was better at this!
  Psalm 91 - Shelter of the most high
  
  
• Playing is a form of service. You also serve the worship leader and the sound team.
  John 13 - Washing of disciples' feet
  
  
• Remember that you're under the authority of the worship leader. You should be accountable to them.
  
  
• In a loose summary of some of all the above points, find a good balance between what the worship leader wants, what the song needs and the way you play (in that order!).
  
  
• There's a (Holy) Spiritual conductor.
  
  
• Be sure to play to the best of the abilities that God has given you. It doesn't matter if you hit a dud note, no bolts of lightning will come down, but your playing (your service) is an offering, you should want to make it as good as you can.
  Psalm 33
  1 Sing joyfully to the LORD, you righteous;
  it is fitting for the upright to praise him.
  2 Praise the LORD with the harp;
  make music to him on the ten-stringed lyre.
  3 Sing to him a new song;
  play skillfully, and shout for joy.
  
  
• Pray.
  

I remember vividly the first time I ever played in a church, it was a little bit different to a gig. The guy leading worship that day was an amazing musician, an ex-pro who'd played and hung out with a number of very well known names (I learnt a lot from him).

I was expecting a big talk about what and how to play, chords, parts, structures, rhythms, but the total of his musical dictum was this; "I don't care what you play as long as you worship". That was it, and that for me is the single most important thing.
Colossians 3:17 "And whatever you do, do it all in the name of the Lord"