So, for one of the current commissions, I was requested to use a real life person's face and turn into an alien. So I dd this as practice for such theme, I used actress Zooey Deschanel as template to make this, eh it came out okay I think.
Art can imitate life, and real sci fi, at least before the advent of CGI, started with real people. Shaak Ti begins with Orli Shoshan, and then we add prosthesis and makeup to make her into a Togruta Jedi Master. So for an artist, I think what easily makes sense is layers. Begin with the human, and then layer on the alien over that.