Using Shell Voicings
A "shell voicing" is a voicing of a chord which leaves out one or more notes, usually the fifth and/or the root. This is useful information for guitarists, as we're often called upon to play chords which, in their full voicings, would have more tones than we have strings or left-hand fingers - or which would be difficult or impossible to reach. Leaving out the less "colorful" chord tones like the fifth and root frees up fingers for more interesting choices like extensions (9th, 11th, 13th) or alterations (b5, #5, b9, #9).
Another reason for stripping down chord voicings is that of texture: in the context of a full band, sometimes a big five or six note voicing is just not what's needed. Using shell voicings can reduce clashes with the other instruments (especially piano) and can un-clutter the sound of the rhythm section. Listen to the work of Freddie Green in the Basie band, for example.
When you're playing solo, shell voicings are invaluable. Joe Pass and Lenny Breau, although their solo styles were quite different, each made masterful use of shell voicings. Bill Evans and Bud Powell, two of the greatest jazz pianists ever, used them extensively in the left hand behind their own right-hand soloing.
In Figure 1, we have sample shell voicings for three chords whose roots are being played on the sixth string. Since no open strings are being used, these are all movable voicings. At the first fret, these three voicings would be for Fmaj7, Fm7 and F7, respectively. They could be used anywhere on the fingerboard according to the chromatic scale: moving them to the second fret would yield F#maj7, F#m7 and F#7; the third fret would yield Gmaj7, Gm7 and G7, and so on. These voicings all have the root on string 6, the seventh on string 4 and the third on string 3. The fifth of each chord has been omitted.
Figure 2 shows the same three chord types, this time voiced with the root on string 5, the seventh on string 3 and the third on string 2. At the first fret, this would result in Bbmaj7, Bbm7 and Bb7.
In Figure 3, we take the shell voicings from Figure 1 and add a "color tone". In this case, I chose an extension, the 13th. This makes the voicing sound fuller and more interesting.
In Figure 4, I used the shell voicings from Figure 2 and gave them the same treatment, adding a 13th to each.
The chord tones are labeled in each diagram. The root is denoted by a white circle, as it may be left out of each chord as well. In a band setting, the bass player will usually be playing roots; the soloist will usually be playing extensions and/or alterations. As a comper, you don't really need to play those things all that often. The third and seventh are all that is needed to imply the quality and function of a chord; this can be a very powerful thing to understand. [In a good band where everyone does their job very well, they don't need you to comp at all: that can also be a very powerful thing to understand.]
You can take it from here. Try modifying the voicings in Figures 3 and 4. For example, the #5 of all those chords would be located one fret lower than the 13th; you could easily change all six of those voicings into versions with an augmented fifth. What if you moved the root up a couple of octaves? In Figure 3, that'd put the root on the first string, at the same fret it was on already. Then the ninth would be only two frets above the root... or how about an F7(#5,b9)?