That's a complex question. The concept of spirit guides came into American occultism from Spiritualism, since most mediums have one. I recommend waiting until a spirit guide shows up, rather than going out of your way to trying to get one, and testing the prospective spirit guide thoroughly before making any commitment to work with it -- there are a lot of parasitic and predatory spirits out there. A spirit guide worth following won't make predictions that turn out to be false, for example.