How are predictions derived from fermisurface ?

As we know that the is an boundary separated the states that are occupied and unoccupied. Moreover, its shape is derived from the periodicity and symmetry of the crystalline lattice. It's said that, for these characters, Fermi surface is useful for predicting the thermal, electrical, magnetic, and optical properties of metals, semimetals, and doped semiconductors. Although I have read carefully Bloch model, band energy, electron on periodic and weak potential, I cannot understand how such prediction can be derive from Fermi surface? Any one can help?