Two more for the list. Low light alone makes them shed leaves they can no longer support, which shows as leggy new growth and gradual yellowing of inner leaves. And simple old-leaf shedding, one or two at a time on a firm healthy plant, which is housekeeping and needs nothing.
And the one thing not to do while you are tidying: leave the peduncles alone. Those stubby spurs where flowers come from look like dead stems in winter, and hoyas rebloom from the same ones. People prune away next year's flowers every January.