Well, for the majority, it’s really a non-issue. All they ever want to do is keep copy-pasting well known stuff, be it some ancient swing or any sub-genre of today’s auto-tuned crap. For the rest of them – the chosen few – here’s the “big secret”. At least if they didn’t already realize what it takes to create something truly new in music; and I bet most of them did.
Anyway, to be innovative musically and churn out something that hasn’t been heard before, you can really only do two main things; here they are.
1. Change the form: While new tunes keep coming out constantly, they all can be identified structurally; the song form is usually something that has been done before, and most of the time artists reach for something that has been done quite a lot. The reason is simple: familiarity keeps listeners in their comfort zone, so they are not forced to have to digest the unknown.
Of course there’s more freedom (and less money) in a couple of genres like jazz or contemporary classical music. Soon you will realize though, that the absolutely new shit you have just invented has been already done before, even if only a couple of times. If your genre happens to be pop music, don’t let the above thing disappoint you, because injecting a known but rarely used musical device into the pop world is often considered innovative, and sometimes it turns out to be successful as well.
Other than the song form, you can come up with your own rhythms or unusual chord progressions and systems; think John Coltrane’s “Giant Steps”.
2. Change the sound: While coming up with a musical form that sounds new in a given era is relatively easy, don’t forget that it’s hard to invent anything this way that has never been done before. But inventing a truly new sound, that’s something that can be done, mostly because of how the audio technology advances. New instruments, new recording and mixing devices keep coming out all the time. The real challenge though is to be able to squeeze something out of your gear that doesn’t only sound new but also pleasant and instantly recognizable.
Another thing to consider when you are going for a new sound is to learn a new playing or singing technique, or emphasize the uniqueness of your style, using the physical (or mental) traits of your own body and system, because chances are you were born with a unique voice, long fingers or have a special touch; anything that enables you to sound like no one else before.