Aspects of a guided surface waveguide probe site and the preparation thereof are described. In various embodiments, the guided surface waveguide probe site may include a propagation interface including a first region and a second region, and a guided surface waveguide probe configured to launch a guided surface wave along the propagation interface. In one aspect of the embodiments, at least a portion of the first region may be prepared to more efficiently launch or propagate the guided surface wave. Among embodiments, the portion of the first region, which may be composed of the Earth, may be treated or mixed with salt, gypsum, sand, or gravel, for example, among other compositions of matter. In other embodiments, the portion of the first region may be covered, insulated, irrigated, or temperature-controlled, for example. By preparing the site, a guided surface wave may be more efficiently launched and/or propagated.