From "Peter Tea Bonsai":
"First off, I removed any brown needles, it’s straight forward.
I normally use a combination of my hands and tweezers to remove the loose brown and yellow needles. They should just come right off when touched.
Old juniper foliage will brown out and fall off ever year on the interior of the branches so it’s perfectly normal to see that happening. Think of old needles falling a pine tree. If the tips of the foliage are browning out, then there’s a problem.
I would either lightly pull (pinch) or cut off the foliage at the base of the branch. I would continue doing this on the rest of the tree.
But! If I wanted to make the branch shorter, I would leave the green at the base and cut the terminal end off."