To learn more about the use of Introductions, let's look at the Beatles' song portfolio. The first thing you notice about Introductions when reviewing the songs found in The Beatles Complete Scores is that many songs do not include an Introduction. The songs simply jump immediately into the verse or, in some cases, the chorus.
Examples of songs with No Intros that start right into the verse include We Can Work It Out, Hey Jude, Penny Lane, Nowhere Man, and The Long And Winding Road while songs beginning with the chorus include Can't Buy Me Love. Another twist on the No Intro approach is to include a count such as in Yer Blues where Ringo is heard counting "two, three" leading directly into the verse. Classic examples of this type of Intro include the Good Lovin' "one, two, three" and the Wooly Bully bilingual "uno, dos, one, two, tres, quatro" countoff.
The Beatles, especially in their earlier songs, made effective use of unique Vocal Intros. The Four Seasons employed these Vocal Intros in most all of their early string of hits.
Several examples of Vocal Intro chord progressions, all transposed to the Key of "E" to permit easier comparison, are shown below.
E-G#m-G-F#m-B7 => E verse progression
Here, There And Everywhere
Em-Am-Em-G-F-B => E verse progression
Do You Want To Know A Secret
Fm-E-Eb-Cm-Fm-E-F#m7-B7 => E verse progression
If I Fell
A-Co-E (3x) E-B-E => E verse progression
P.S. I Love You
C#m-F#7-A-E => E verse progression
She Loves You
The Beatles frequently created Instrumental Intros by using the following techniques:
(1) Use the beginning chord of the ensuing verse or chorus. On Yesterday, Paul McCartney's two bar "F" chord Intro, played on an acoustic guitar, leading to the "F" (I) chord of the openning verse is simple but created an instantly recognizable Intro. This technique was also used on I Saw Her Standing There where The Beatles simply played an "E7" chord for four bars leading into the verse progression that begins with an "E7" (I7) chord for two bars.
(2) Use a dramatic Opening Chord such as the "D7sus4" (V7sus4) that begins A Hard Day's Night. Other examples of this technique include the "E7" (V7) to start Rock And Roll Music, the "E+7" (V+7) to kickoff Oh! Darling, and the "A" (V) chord in She Came In Through The Bathroom Window. The use of a "V+7" was definitely inspired by various Chuck Berry song Intros.
(3) Restate, in whole or part, the verse, chorus, bridge, or turnaround. In Let It Be the Intro was created by playing the first four bars of the openning verse without vocal accompaniment. On Please Please Me the first two bars of the openning verse were repeated with the melody played on harmonica. Twist And Shout begins with the first four bars of the openning verse played without vocals or melody.
On I'm Happy Just To Dance With You The Beatles created a four bar Introduction by repeating the first two bars of the verse progression (C#m-F#m-G#7). An example of using a Turnarond as an Introduction is the one bar descending bass line "F-Eb-G/D" (IV-bIII-V/5th) progression used in Something leading into the verse progression that begins with a "C" (I) chord.
(4) Create an Introduction that is unique from the other parts of the song such as the instantly recognizable "Dadd9-E/D-G6/D-Dadd9" (Iadd9-II/b7th-IV6/5th-Iadd9) Intro to Eight Days A Week which was also used as it's Ending. Another example is the "C-D (3x) D7" Intro to I Want To Hold Your Hand. Other unique Intros are created by the use of freestyle arpeggios or lead solos, usually without the full band. Revolution was created using a Chuck-Berry-on-acid guitar solo. This guitar solo approach was also used on Drive My Car. For other variations, check out the Trumpet/Brass Intro on Got To Get You Into My Life and the clarinet solo on When I'm Sixty Four.
With the above techniques you should be able to spice up and improve your song Intros.