Mohit,

It highly depends on actual circuit, which has to be protected!
Also, keep in mind, that varistors can only be used for a rough voltage limiting. Means, in an ESD event even with varistor heavy overvoltage can be produced! E.g. SIOV-S10K14 (epcos) which was often used for car applications, accepts maximum applied voltage of 14Veff (18Vdc). But it firstly opens at 22Vdc (1mA)! Taken into account manufacturing tolerance, turning-on voltage can increase up to 24Vdc (1mA). But with ESD event, where for a very short time dozens of Ampères can flow through varistor, even much higher overvoltages can be observed: 36V at 1A, 45V at 10A and 68V at 100A. This must be keept in mind, when using varistors.
So, if your circuit to be protected can accept these overvoltages, everything is fine. But if not, additional measures are needed. E.g., you could use additional protection diodes connected from input signal to supply voltage and 0V, behind the varistor and in combination with current limiting resistor. This leads to a two step protection circuit: First rough limiting, second fine protection.

Additionally:
ESD events are very very fast. For protecting you need a decive, which turns on in less than 1nsec! A varistor with leads CANNOT do that, it needs about 10nsec for turning-on! Only a SMD varistor can act so fast.
Also, varistor element must be connected in a certain way, so that voltage drops from ESD currents running over copper traces are NOT added to limited signal voltage:

--------------------------V--------------------------
                          a
                          r
Input                     i                          Output
                          s
                          t
                          o
--------------------------R--------------------------

Locate varistor as near as possible to input of circuitry, so that copper traces carrying ESD currents are as short as possible.

But again, how to protect a circuit cannot be told in total detail without knowing the circuit.

Kai