I've grown/killed several of these, try to find out:
If your Juniper needs Acidic or Alkali water, your tap water may be incompatible. (also, sometimes Chlorine can be bad for some bonsais)
Keep it out of drafts.
Make sure that it gets plenty of sunlight, but not TOO much DIRECT sunlight.
Is your plant in an organic medium, or glued stones? You may need to give it nitrogen fertilizer once every two weeks. An OTT light (compact flouro) may help with supplemental light.
Overwatering, WILL kill a plant, the more water that stays in the pot, the less oxygen can get to the roots. Yes plants MAKE oxygen, but they NEED oxygen at the roots for osmotic transfer of nutrients and such.
Just remember, nothing good will happen fast with anything that grows!!!
-SF