Getting back to the OP's question.
Lots of good information already provided in this thread.
The bottom line is you want the contact angles between the sear and hammer to remain the same, but you want all of the sliding surfaces to have as little friction as possible.
Al brings up a good point when he writes, "I leave mine alone. They work." When you get right down to brass tacks, you really don't need to do anything.
Most of the resistance to the hammer release occurs where the sear is sliding off the hammer hooks while the parts are being forced together by the hammer spring. Therefore, polishing the sear contact surfaces (without altering the angles) yields the most results in reducing trigger pull weight.
Once you get the sear nose and hammer hooks polished so that there is little friction between those surfaces, the next step is to reduce the friction in all of the other parts involved.
Starting at the trigger, the trigger and trigger bow should slide in the frame with no resistance. Once that is taken care of, we move our attention to other parts.
The sear spring acts on the disconnector and sear. Those contact points should also be smooth. The spring itself is usually heavy enough and doesn't need to be altered.
The sides of the sear should be polished, so it doesn't drag on the frame.
The last step is to place a tiny bit of white lithium grease on the nose of the sear. Because the sear and hammer are being forced together by the hammer spring, that sliding force is relatively heavy. A tiny bit of grease will help to keep that friction to a minimum.
Reducing the weight of the hammer spring is a double edge sword. While that can reduce the pull weight a little because it reduces the force needed to slide the sear out of engagement with the hammer, it also increases lock time and can reduce reliability of primer ignition. So, tread carefully when reducing hammer spring weight.