The pole must be positioned either above or below the dominant pole of the driven system (transistor and whatnot). Usually by a factor of 3 or so.
Or better yet, a pole-zero pair (using an R+C instead of C alone) can be positioned so that the zero cancels the system pole, and the remaining dominant pole sets the desired/required roll-off frequency.
I don't know what your transistor is driving, but a typical example would be a constant current sink, where the series resistor and gate capacitance form a dominant pole.
Tim