Key features that I look for in quality piano accompaniment tracks were covered pretty thoroughly in a previous post. Of course, these features can be applied to any sort of accompaniment regardless of instrument(s) and I attempt to incorporate them into my guitar accompaniment as appropriate.
As I have mentioned in other posts, I try to supplement the use of piano recordings with live guitar. This provides some variety for our music worship and is often necessary because I can not find a good quality piano track for the song I want to use. In addition to the techniques discussed previously, here are a couple of techniques that I find useful when accompanying on guitar.
1. Suitable intros (revisited)
I have observed that in many churches today, especially those employing “worship leaders” and a “praise band”, that the guitar is becoming more commonplace as the accompaniment instrument of choice. Of course, a lot of the modern “praise and worship” music is often guitar-based to start with.
However, I have noticed that in some instances, the guitarist will often start a song by simply strumming or picking the first chord (or progression) without providing any musical cues to the congregation such as a snippet of the basic melody and/or starting pitch. It is possible that he/she could be staying true to the original composition of the song which may not have these cues in the intro. This may work fine for those who are already familiar with the tune but can be more of a challenge to those who may have never heard the song before or have difficulty identifying the starting pitch.
I realize that the lack of starting pitch or melody preview is probably only going to be an issue for the first few notes or so, but when you only have a relatively small number of folks in the congregation, the music leader may end up singing the first few notes solo until folks catch on to the pitch and melody. Believe me, this is very noticeable in a small congregation but probably not an issue in a larger one. If folks are unsure of the starting pitch of a song, they are going to hesitate until they hear others start to sing.
To help alleviate this potential awkwardness at the start of a song, I simply follow the same technique as a good pianist would employ: play the last phrase or two of the song to establish the key, tempo, and cue for the starting pitch. Once you do this and bring the congregation in successfully on the right pitch and tempo, you can usually settle in to a strumming or picking pattern for the chord progression of the song without the need to keep playing the melody line.
Of course, this assumes a certain level of proficiency for the guitarist. In other words, he/she may or may not be able to play a chord-melody intro. However, I believe that, with a little practice, they should at least be able to play a single-line melody intro to help the congregation find the starting key and pitch. This may sound a little thin initially but hopefully it will provide enough of a cue to start the song. Then they can just launch into whatever strum/picking pattern they are comfortable with. Since I primarily play chord-melody style on a regular basis, I usually try to employ that technique for the intro to get a fuller sound and help establish the key signature.
2. Strumming and picking techniques to clarify tempo
I have also found that it is very important for the congregation to clearly hear the beat of the song so that everyone stays on tempo. Choosing a good strumming or picking pattern can facilitate this in the absence of percussion or piano (which is percussive by design).
For faster, more upbeat songs, I generally employ a bass-chord-bass-chord style for 4/4 timing where the beat 1 bass note is the root of the chord and the beat 3 bass is an alternate bass note within the same chord. For example, when playing an open Gmaj chord (1st position), I will play a measure as follows:
Beat 1 – Pick G bass note (6th string)
Beat 2 – Strum strings 1-4 together as chord
Beat 3 – Pick B bass note (5th string) or D bass note (4th string)
Beat 4 – Strum strings 1-4 together as chord
For an open Dmaj chord, I will alternate between the D bass (4th string open) and the A bass (5th string open). Admittedly, this technique does lend a bluegrass feel to the song but I like gospel-bluegrass so there you have it. 
For faster tempo songs in 3/4 timing, I generally use a bass-chord-chord pattern. These patterns are rather simple but I try not to get too fancy since I want folks to pay close attention to the message of the song and not my technique. The main goal is to keep the rhythm/beat of the song clear so that we all stay together.
For relatively slower songs and especially 6/8 timing, I use arpeggios or various picking patterns to keep a smooth flow and add melodic variety. Straight strumming of chords on slower songs often sounds rather lethargic in my opinion. Regardless of the time signature, I will still pick a root bass note on beat 1 so that the chord voicing is clearly stated along with the notes to follow. If there is a chord change within a measure, just make sure to hit that root bass first either alone if the chord is played across multiple beats or with the complete chord if it only transitions for a single beat.
This post is not intended as a guitar technique tutorial but I just wanted to give a couple of examples to clarify how I usually accompany. My apologies to any seasoned guitarists who are already familiar with these techniques. If there are any beginner guitar accompanists who need further clarification on these suggested techniques, please comment accordingly and I will try to help.
The Accidental Hymnologist 