Consider that an ESD "strike" causes a large amount of current to flow from one node (wire, signal, etc.) to another, and that neither of these nodes might be ground. The goal of the ESD protection scheme is to provide a safe path for the ESD current, which can be many amperes for a short time, away from the sensitive circuits in the product. By providing paths from every node to a common point, usually ground, ESD currents are given a safe loop to flow through and dissipate.
In IC design, we pay much more attention to the input/output pads and their circuits than the interior circuits in the chip, but in a board level product design you need to pay attention to all the wires and traces on the board. We usually draw a schematic of the system and examine where ESD current will flow between every pair of nodes (choose one node as positive and another as the negative return point... even if the "loop" is closed outside the product the danger is from large current flow or large potential differences between nodes in the product). You don't need to worry as much about passive components, unless they are small RF transistors or diodes, but ICs are always ESD sensitive.
You can consider adding ESD protection devices (diodes or TVS's) to ground at points where ESD current would otherwise flow through a sensitive circuit. The diagram in the Semtech ESD .pdf linked in Dejvid_n01's post shows an example. Generally you want devices with a low forward voltage drop, since high voltages generated by the ESD currents can damage ICs. Also, it's important to consider current flow in either direction; the TSV devices provide low voltage drop in either direction.