There are permanent dipoles present in polar dielectric which are randomly aligned in such a way that there is permanent dipole moment Pp. [see fig a]
When a dipole is present in an uniform electric field the dipole tries to align itself in the direction of electric field.
Because of this all dipoles in a polar dielectric are partially aligned in the direction of field. This partial alignment is responsible for the induced dipole moment Pi.[see fig b].
Therefore, the electric dipole moment is increasing.
P = Pp + Pi
The electric dipole moment of a polar dielectric increases
a) by increasing the applied E.
b) by decreasing the temperature