Summarize:

Thoroughly water the juniper in its container, soaking the soil and making it more compact.  Feel the soil in the container before you do this. If it already seems very moist and very compact, you should skip this step. Watering the soil reduces the amount of air in the container and makes it easier to remove the root ball. Use a shovel or spade to dig a hole that is twice as wide and at least as deep as the container the juniper plant is currently in. There needs to be plenty of space. If you make a hole that is just barely big enough, the roots may not settle and establish themselves well. Mix 2 tsp (10 ml) of a balanced 10-10-10 fertilizer into the soil for every 1 gallon (4 L) plant.  Note that a 10-10-10 fertilizer refers to a blend containing equal parts nitrogen, phosphorus, and potassium. You should either mix the fertilizer into the soil at the bottom of the hole or spread it around the outside of the hole. Do not lay the fertilizer directly inside the planting hole. If the plant is in a disposable plastic container, carefully tip the container on its side and press around the outside to loosen the soil and root mass inside. You should be able to carefully slide the entire soil mass out of the container with your hands or shovel. If the plant is not in a disposable plastic container, you may need to loosen the soil around the sides of the container by gliding your shovel around the inner perimeter. Use your hands or a dull knife to separate the individual roots from the compacted mass. Loosen as many of the roots as possible without damaging too many. You do not need to tease out all of the roots, but the longer ones at the bottom of the root ball should be loosened from the mass. This will help the roots spread into the surrounding soil as you plant the shrub. Place the root ball in the center of the hole you dug. The top of the root ball should be level to the surface of the soil around the hole. The soil level should be about the same as it was in the pot. If you discover that the planting hole is too deep, take the plant out and add more soil before putting it back in. If the hole is too shallow, remove the plant and dig the hole deeper before returning it. Hold the shrub steady and upright while you fill in the hole around it with some of the soil you removed while digging the hole.  You can also add some organic matter during this time, but that is strictly optional. Pat down the soil with your hands or feet to settle it and remove any air pockets. Do not stamp the plant into the ground, however. When junipers are planted too close together, a thick layer of foliage can form, causing problems with air circulation. As a result, the plants are more likely to face problems with pests and diseases.  This can be a problem for all juniper varieties, but it is especially problematic for horizontal growing varieties. The exact amount of space you need to leave in between juniper plants will vary based on the type and size of the variety you choose. Consider how far the shrub spreads and space the plants wide enough apart to prevent them from spreading into each other. Give the plant plenty of water immediately after you finish planting it. Doing so will help the plant establish itself while further compacting the soil. Continue to water the plant twice a week for the first month to help it establish itself.
Water the juniper in its container. Dig a large hole. Mix in a balanced fertilizer. Remove the plant from the container. Loosen the root mass. Place the root ball into the hole. Fill in the rest of the hole. Leave plenty of space in between plants. Water thoroughly until established.