I've been wondering how to go about describing different alien species' appearance. How much depth should I go into when describing them? I don't want to be like "And it's got a rigid plate protruding from its head at a rough 45 degree angle and it has three eyes on either side of its head that are spaced about 8.5 centimeters apart and..." But then again I want people to know what these things look like, what do you think? Admittedly I'm more of a fantasy reader than sci-fi but my stories always come out as sci-fi, so maybe I'm just lacking in good examples. As a further question then, what are some decent sci-fi novels that could help me in this department?