What is an easy way to teach my dog gee and haw?

I have a german shepherd who is three years old. She is one strong dog ! And I am trying to be creative, and teach her to pull a sled. She is very scared of the sleds, and tries to run off, but i think that i can get her used to them. I know that german shepherds arent meant to pull sleds, but this is just a fun activity. I am trying to teach her the basics of gee and haw by just walking her around the yard, and when i turn, i say either "gee" or "haw" . But she isnt learning anything. I have a harness for her, and a sled, and a long leash for it, but I have no idea what to do, and i dont know where to begin .