2D materials with honeycomb lattices are increasingly studied due to their unique electronic and mechanical properties. The typical preparation techniques, such as chemical vapor deposition and cleavage of bulk crystals, are either complicated or limited to only certain classes of materials. Here we discuss basic ordering principles in 2D monoatomic layers and show that electrochemical deposition can also result in 2D films with desired honeycomb structures. The principles are first studied on model ionic 2D layers prepared in ultrahigh vacuum. Two ordering possibilities are identified: a bilayer structure for covalently bonded films and a mixed monolayer structure for ionically bonded films. Typically, the most energetically favorable configuration in mixed layers is when ions with one polarity are closely surrounded by ions of the opposite polarity. This translates into a layer with honeycomb structure on substrates with p6/p3 symmetry. This phenomenon can be used to prepare germanene, a layer with such a structure.