It is somewhat of a shame that the most common type of voicing used by most pianists since the 1950′s has no well established name. I have seen these type of voicings called Category A and Category B voicings, Bill Evans voicings, or simply left hand voicings. Because they are based on the third and seventh of the associated chord, I call them 3/7 voicings.
The basis of these voicings is that they contain both the third and seventh of the chord, usually with at least one or two other notes as well, and either the third or the seventh is at the bottom. Because the third and the seventh are the most important notes that define the quality of a chord, these rules almost always produce good sounding results. Also, these voicings can automatically produce good voice leading, meaning that when they are used in a chord progression, there is very little movement between voicings. Often, the same notes can be preserved from one voicing to the next, or at most, a note may have to move by step.
For instance, consider a ii-V-I progression in C major. The chords are Dm7, G7, and Cmaj7. The simplest form of the 3/7 voicing on this progression would be to play the Dm7 as “F C”, the G7 as “F B”, and the Cmaj7 as “E B”. Note that in the first chord, the third is at the bottom; in the second chord, the seventh is at the bottom; in the third chord, the third is at the bottom. Also note that, when moving from one voicing to the next, only one note changes; the other notes stay constant. This is an important characteristic of 3/7 voicings: when they are used in a ii-V-I progression, or any progression in which root movement is by fourth or fifth, you alternate between the third and the seventh at the bottom. An analogous set of voicings is obtained by starting with the seventh at the bottom: “C F”, “B F”, “B E”.
Normally, you would use more than just the third and seventh. Often, the added notes are the sixth (or thirteenth) and ninth. For example, the C major ii-V-I could be played as “F C E”, “F B E”, “E B D”, or as “F A C E”, “F A B E”, “E A B D”. The added notes are all sixths or ninths, except for a fifth in the first chord of the second example. When playing these four note voicings on guitar, any added notes will usually be added above the third and the seventh, or else your voicing may end up containing several small intervals, which is usually possible to play only with difficult hand contortions. Thus, the C major ii-V-I might be played with four note voicings on guitar as “F C E A”, “F B E A”, “E B D A”.
Note that none of these voicings contain the roots of their respective chords. It is assumed that the bass player will play the root at some time. In the absence of a bassist, pianists will often play the root in their left hand on the first beat, and then one of these voicings on the second or third beats. Actually, you can often get away with not playing the root at all; in many situations, the ear anticipates the chord progression and provides the proper context for the voicing even without the root. It is not forbidden to play the roots in these voicings, but it is neither required nor necessarily better to do so.
These basic voicings can be modified in several ways. Sometimes, you may wish to omit either the third or the seventh. Often, a minor of major chord that is serving as a tonic will be voiced with the third, sixth, and ninth, and these voicings might be interspersed with regular 3/7 voicings. Also, voicings with the fifth or some other note at the bottom can be interspersed with true 3/7 voicings. This might done for any of several reasons. For one thing, when played on the piano, note the voicings described thus far all tend to slide down the keyboard as the roots resolve downward by fifth. The normal range for these voicings is in the two octaves from the C below middle C on the piano to the C above middle C. As the voicings settle downward, they will start to sound muddy, at which time you might want to jump up. For instance, if you have ended up on a Dm7 as “C F A B” below middle C, and need to resolve to G7 and then Cmaj7, you might want to play these two chords as “D F G B” and “E A B D” respectively to move the voicing upward while preserving good voice leading. Also, roots do not always move by fifths; in a progression such as Cmaj7 to A7, you might want to voice this as “G B C E” to “G B C# F#” to preserve good voice leading.
One thing to note about these voicings in the context of a diatonic ii-V-I is that, because the chords imply modes of the same scale (D dorian is the same as G mixolydian is the same as C major), a given voicing can sometimes be ambiguous. For example, “F A B E” might be either a Dm7 with the seventh omitted, or a G7. In the context of a modal tune like “So What”, it clearly defines the Dm7 or D dorian sound. In the context of a ii-V progression, it probably sounds more like a G7. You can use this ambiguity to your advantage by making one voicing stretch over several chords. This technique is especially useful when applied to the more general scale based voicings discussed later.
Another thing you can do with 3/7 voicings is alter them with raised or lowered fifths or ninths. For instance, if the G7 chord is altered to a G7b9 chord, then it might be voiced as “F Ab B E”. In general, the notes in the voicing should come from the scale implied by the chord.
These voicings are well suited on the piano for playing in the left hand while the right hand is soloing. They can also be played with two hands, or with all strings on a guitar, by adding more notes. This provides a fuller sound when accompanying other soloists. One way to add more notes is to choose a note from the scale not already in the basic voicing and play it in octaves above the basic voicing. For instance, on piano, for Dm7 with “F A C E” in the left hand, you might play “D D” or “G G” in the right. In general, it is a good idea to avoid doubling notes in voicings, since the fullest sound is usually achieved by playing as many different notes as possible, but the right hand octave sounds good in this context. The note a fourth or fifth above the bottom of the octave can often be added as well. For example, with the same left hand as before, you might play “D G D” or “G D G” in the right hand.
The 3/7 voicings are perhaps the most important family of voicings, and many variations are possible. You should try to practice many permutations of each in many different keys.