Well firstly you need to ensure you have a male and female. Then you need to wait until the male is significantly larger than the female. Otherwise she will likely not breed. The female will need to be around 2" or larger. The male will generally be quite aggressive to the female to begin with, until she gives in. Then they will flare and shake at eachother, biting rocks etc. They usually spawn on an open area, usually a rock on a gradient around 45 degrees.
Why do you ask? Are you planning on trying to breed some?