Rubbertree plants are from tropical climates, so try to mimic that climate for the healthiest plant.
Keep them in a warm spot (not in direct sunlight). They'll not do well in cold or drafty areas.
As for watering, saturate the soil with water and then let it dry out most of the way before re-watering. The natural tropical climate usually has periods of rain and then periods of dryness.
Prune the tree also, cutting above the nodes here or there.