How Do I Develop a New Character?

I start with an idea in my mind, or I may even have already written the story about them, giving them a particular set of physical characteristics.

In this case, a German Shepherd with atypical ears, some might say they are a little wonky. I think they are perfect. She is called Lugs: Lizzie Lugs.

If I can, I will source reference photos; if not, I will take them myself.