Creating pleasing silhouettes is much easier than you might think. Look back through this blog, and you will find that my exposure settings for silhouettes are almost always the same. I always point my camera to the brightest part of the sky and set the ISO to 400, aperture to f/5.6 and shutter speed to 1/5,000 of a second; this will always produce a sharp and noise-free image.
In post-capture processing, I slide the black point and shadow slider to ensure my subject is black. I usually slide the colour temperature to the right - remember this is a creative process and adjust to taste!