Junipers usually look good once planted and after a while decline due to lack of sunlight, winter injury, vole damage, http://extension.umd.edu/hgic/voles possible diseases, poor drainage, etc. Junipers grow best in full sunlight and a well drained soil. They can be susceptible to root rots if the soil is heavy and does not drain well. You will have to check for this. Make sure mulch is no thicker than several inches and kept away from the base of the plants. All you can do is remove any fallen leaves to improve the air circulation and prune dead wood. The plant will put out new growth where there are green leaves only.
You can send us digital photos of the plant so we can see what you may be dealing with.