Generally speaking, improving a 1911's, or any gun's, trigger pull involves more polishing than cutting or grinding. It is a job for fine-cut files and fine-grit stones, and it is a finicky job that must be done carefully and exactly right.
The first step is to true-up the mating surfaces of sear and hammer. The hammer-notch's surface must be set exactly upon a radial line that originates at the center of the hammer's pivot point. The sear's face must be exactly tangential to the sear's pivot. Both surfaces must be dead flat.
The final step is to polish both of these surfaces until they are both absolutely smooth and slick, while at the same time maintaining the angles you have so carefully already trued-up.
A possible further step might be to also polish the contact surfaces of the trigger's and sear's spring leaves, part of the three-leaf flat spring within most 1911's handles.
As you might be able to understand from this description, this is a job best left to an experienced pistolsmith.
I suggest that, when interviewing a prospective pistolsmith, you ask whether he cuts, grinds, or otherwise alters any spring, particularly the hammer's mainspring. If the 'smith admits to cutting or grinding 1911 mainsprings, go somewhere else.
I have no idea what this work costs nowadays. However, good work is not cheap.