Place your gardenia in an area where it will receive half a day of direct sunlight. You could place it near a south-facing window.
This will be especially challenging if you brought the gardenia inside during winter, when sunlight is scarce. One option you could take would be to supplement what little sunlight the plant receives with a grow light.
The gardenia will also need to be in a room with a temperature of 55 °F (13 °C) during the day and 64 °F (18 °C) at night.[16] Adjust your house's thermostat accordingly and monitor your Gardenias' growth.
Keep your plant free of drafts and never place a gardenia where it will receive direct force of hot hair from a furnace. The drying nature of the heat could cause your gardenia to literally fall to pieces.