WildChild

A lot of my tress are Junipers, and here is what I have learned (I live in Sydney, Australia by the way):

-Never over water. Junipers prefer to be a bit drier.
-Which leads me to my next point that your soil mix should be free draining. My soil mix for Junipers is a 60:40 ratio of Grit to Peat, with a small about of bark sifted through.
-They love the sun, but the shade as well. While no one is home during the day, the tress are taken from their places and put in strategic spots - spots that will be in full sunlight for half the day and shaded for the other half.
-Never water in the middle of the day. Give them a drink in the morning so they can get through the day. Give them another drink at around 5-6pm to replenish the water they lost. Again - only if the tree needs it. And only do this in summer. However, down here, the average winter temperature is 23C, So your habits may be different.

Hope this helps, and scratch the bark under the green bits. If it is looking fine, then you best prune away the die-back and have another go. If not - bad luck, its all part of the learning process! I agree with Pootsie, a Ficus/Fig is the way to go. It is nearly impossible to kill them.

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"Creating bonsai is not a mechanistic process; we prune with the hand but are guided by the heart..."