From “The Essential Secrets of Songwriting” website
We tend to think of energy as a value that we give an entire song: “That song has lots of energy…” or “I think that other song needs more energy…” etc. But to be a successful songwriter, you need to be thinking on a more focused level about energy. And consider the fact that energy is something that fluctuates throughout an entire piece of music.
How that energy ebbs and flows will determine if your listeners stick with it and listen to your song all the way through.
Generally speaking, energy levels should increase as your song progresses. Choruses really do need more energy than verses, and bridges require more energy than choruses to really work.
How important is this? It is vital. By carefully crafting the energy of your song, you make it feel that something exciting is about to happen. Energy should build through the verse, making the chorus feel like it belongs. By having energy ebbing and flowing randomly, your song will feel directionless and boring.
So how do you control the energy of your songs? There are several key ways:
1- Dynamics (loudness). The louder your music, the more pent-up energy the listener will perceive.
2- Instrumentation. The more instruments you use, the more vigorous and full your music will sound.
3- Range. The higher the notes, the more energy is sensed from the music.
4- Rhythm. You’ll feel a much more intense energy coming from busier rhythms.
If energy isn’t something you’ve really considered before, now is a good time to go back and make a chart of the basic energy level of the various sections of your songs. You may find ways to finally inject some well-needed energy into an otherwise tiresome tune!