I come up with these ideas when I'm sitting at my desk doodling/sketching. Most of my stuff is pokemon-related but on occasion I'll come up with some creatures and give them names and put them on this list. I'm also an avid astronomer and took numerous astronomy courses since high school, so I'm fairly knowledgeable on the circumstances you'd have to have for a planet to be able to harbour life, and how said creatures would evolve to their planet. Coming up with names for ores is just searching for synonyms of a normal word, I'll take for example "Luminite", I went with a synonym for "glowing", in this case "illuminate" and added "-ite" where it sounded best (-ium also works).
As for the planets I just use my old textbooks, Wikipedia, or Hubble's website.