Put the Japanese juniper in a place with several hours of full sun. Find a location near a south-facing window or in front of a sliding glass door.
Apply a general purpose fertilizer every year at the beginning of spring. Follow the directions on the label.
Add water regularly when the top 1 to 2 inches of soil is dry, saturating the soil until the water drains from the bottom of the pot.
Replace 1 to 2 inches of potting soil or compost every spring in the years you don't need to transplant the Japanese juniper. This adds needed nutrients.
Transplant the Japanese juniper when the plant outgrows the pot. Use a pot 4 inches wider and a well-draining potting soil, and always bury the plant at the same level in the soil.
Prune the Japanese juniper only as needed to control the shape or to remove damaged foliage.