To keep the leaves shiny and healthy mist them or wipe them down with a wet cloth. In colder seasons your Ruby Rubber Tree will need less watering; if the leaves start to brown or yellow and fall off then you could be overwatering.
Anywhere within room temperature ranges (often between 60-75°F) is good, but make sure that you don’t keep it too cold, or too close to any heat or AC vents.
There are no extreme measures needed regarding humidity for a Variegated Rubber Tree. Normal humidity is often fine, and if a room is too dry, then increase misting the leaves or set up a humidifier.
Never fertilize your plant during the colder seasons, but it’s safe to fertilize in Spring and Summer. One recommendation is to use “diluted liquid fertilizer” every couple of weeks.