Earth is the right distance from the sun, such that liquid water has been stable in significant volumes over much of the planet's lifetime. It has the right chemical ingredients for life (e.g. water and carbon), and chemical cycling (such as between the planet's interior and oceans by volcanism and other geological activity) provides chemical pathways for life to extract energy to survive.
Additional factors that have allowed the evolution of complex life are an oxygenated atmosphere, and protection from solar radiation by its magnetic field.