Nuke, what exactly are you going for? Smooth? Light? Least amount of travel? or D all of the above?
Smooth, I'd polish all of the contact surfaces including roll pins if you can get to them.
Light, is going to be part polishing (light springs but sand paper contact surfaces will be like shooting a Taurus Millennium pistol) Trigger spring is 1 place but you also have the sear spring itself you could play with if you are willling to risk it.
Least amount of travel, you'd need to install & configure a set screw.