I've never heard of a moonlight variety but then again I don't know all the varieties of junipers. However, by your description, your plant already has a spiral shape.. maybe a bit overgrown, but there is still some discernable shape. Take very visible twine and line the plant following the spiral. Take a pair of pruners or scissor and start trimming starting from the innermost portion first. Once you are satisfied with the depth and you start seeing a shape, slowly work yourself outwards. Keep in mind that it will take the plant very long to recover should you trim off a major branch. So take your time and do not hardprune. Stand back often to observe your progress. I would advise that you look into some topiary books, even if you should only read them while visiting a bookstore.. Read up on techniques of trimming the plant. It's very difficult really. In fact, in your case the shaping has already been done for you and all you need to do is to follow the shape.