Music is only interesting when there's contrast. Here's a few ways you can create contrast in your music:
Loud vs. soft
- Sound vs Silence
This is really just an extension of dynamics, but in practice it's quite different
The tone and mix of all the instruments together
The way a specific instrument sounds
Which instruments play which parts.
Pretty self explanatory. Use different rhythms, time signatures, etc.
The difference between consonant and dissonant notes/chords
The volume of each note over time. For instance, a drum has a very fast attack (the pop) with a fast decay and a very quiet sustain that lasts a second or so. On the other hand, the human voice has a long attack that sounds almost like a fade in. You can vary the envelope using dynamics processors like compressors.
There are also a few ways to create additional contrast that you can add in post production.
Moving the sound from left to right. This is a HUGE thing in mixing. One of the most common things amateur musicians do wrong when mixing their own music is leaving everything panned center, or very close to center.
- Stereo Width
How far the tracks are panned on average, from a plain mono sum of all the tracks, to an ultra-wide mix with nearly every track panned all the way to one side or the other.
The balance of frequencies.
That all being said, keep in mind that repetition is what makes music memorable, and familiar. For a few ideas on how to create lots of contract and still have repetition just listen to your favorite song. If it didn't have both of those things, you wouldn't like it (I can't say for sure since I probably don't know you, but if you're like every single person I've ever met it's true *wink*)
All in all what makes music interesting is contrast and repetition. weird huh?