Often it can be difficult to come up with a structure for a piece of music (or dance, film, other time based arts) that doesn’t conform to conventional models. That’s not to say that convention is bad per se, but it’s good to be able to choose how you’re going to do something, rather than say “oh, I’m writing something classical, it has to be a sonata or a rondo or a theme and variations”.
Below is a list of processes that occur in time, which processes like the elaboration of sound or movement ideas might follow, to help you generate the form for a piece, or to help you add some kind of structural subtext to other formal ideas of your own, or that are pre-existing.

Storytelling
Learning
Building
Decaying
Growing
Evolving
Remembering
Creating
Speaking
Ageing
Travelling
Sex
Assembling
Unwinding
Hardening
Softening
Moving
Stopping
Heating
Cooling
Revealing
Concealing
Pursuing
Leading
Turning
Metamorphosing
Expanding
Contracting
Accelerating
Decelerating
Crescendo
Decresendo
Changing
Repeating
Reproducing
Gestating