I assume that you already have taken both partial derivatives.
When we want to find a suitable integrating factor, sometimes it's not so easy, so we may introduce the following cases.
CASE I. Integrating factor dependent of Suppose that
it's a function that depends only of
which we'll denote it by
Then, an integrating factor for the given equation is
II. Integrating factor dependent of
If we have that
it's only a function of
is an integrating factor for the differential equation on the form
III. Integrating factors of the form
If they exist
is an integrating factor for the differential equation mentioned previously.
IV. If they exist functions
then an integrating factor for the differential equation is
Note that the case IV includes to the cases I, II y III if we take