For me it was easy. I kept seeing a lion that called himself "Marbas" in my dreams. When I didn't, I saw a sigil in my dreams, usually carved onto a door or wall. I did some digging, as I was new to the Goetia at the time, and there it was. *shrug* That's all there was to it.
The funny part is a couple weeks later, a friend of mine was coming in from out of town and presented me with a gift of an ultra-cute (you guessed it) stuffed lion. (IMG:
style_emoticons/default/wink.gif) I figured it was a sign. (IMG:
style_emoticons/default/wink.gif)
I've never formally called him yet, but I'm not sure if I need to either. He's always just kind of there for me.