Change the key.
Modulation is how music moves from one key to another. A chord that belongs to both keys acts as a pivot — the hinge where the listener's sense of "home" shifts. One moment you are in C major. The next, without knowing when it happened, you are in G major.
The listener needs to feel settled before you can move them. A cadence or two in the starting key anchors their ear. Without this, the modulation has nothing to depart from.
A pivot chord is diatonic in both keys. It is simultaneously one thing and another. The Am chord is vi in C major and ii in G major. When it sounds, both interpretations are valid. The next chord decides which reality wins.
After the pivot, a dominant-to-tonic cadence in the new key locks it in. The V7 chord of the target key contains the leading tone — the note that pulls irresistibly toward the new tonic. Once that resolves, the modulation is complete.
Closely related keys — one fifth apart — share six of seven notes. The modulation is so smooth it can happen without the listener noticing. This is why pop songs modulate up a fourth or fifth for the final chorus.
Distant keys share fewer notes and require more dramatic pivots. A chromatic mediant modulation (up or down a major/minor third) creates a cinematic shift — same chord quality, different root, maximum surprise with minimum chaos.
The relative minor and its major share all seven notes. Moving between them is less a modulation and more a change of perspective. Same landscape, different vantage point.
Truck driver modulations — shifting the whole song up a half step or whole step — are blunt but effective. No pivot chord needed. The lift itself is the emotional payload. Whitney Houston, Bon Jovi, every power ballad.
Enharmonic modulation exploits the fact that some chords can be respelled. A German augmented sixth chord is enharmonically identical to a dominant seventh. One resolves inward, the other outward. Same sound, different destination.
The best modulations are the ones you feel before you understand. Theory names the pivot retroactively. The ear knows first.