Unless there is a hitch or something when cycling in double action I would stay away from the hand, the extractor star, the trigger and hammer surfaces. Hammer and trigger sears are usually very good in the first place and in the second very easy to ruin. Same with extractor star, if it times correctly leave it alone. Sometimes there are small burrs or rough spots in the frame where the rebound slide runs. Those can be polished up a bit with a small fine stone. Same with the bosses that surround the trigger and hammer studs in the frame and side plate. These can be touched up. But, a bunch of dry firing is better to do first. For one thing it will cause any high spots or burs show up as shiny wear arcs on the side of hammer/trigger. You don't need to polish anything completely smooth, just get rid of high spots. Most S&W revolvers have decent triggers to start with.

A reduced power rebound sspring helps as long as the trigger still positively resets. I don't replace the hammer spring. There are several things you can do there though. Turn the hammer spring screw out a turn and fire a 12 rounds or so. If they all fire, turn it out another 1/2 turn and try again. When it starts to miss fire turn it back in 1/2 turn and try again. DO NOT LEAVE THE SCREW LOOSE. Instead turn it tight counting every 1/4 turn. Remove screw and measure with good calipers. Every 1/4 turn is .078 of length on a 32 to the inch screw. Multiply number of 1/4 turns by .078. lets say, 3/4 of a turn. this would be about. 023. File that much off screw leaving tip just slightly rounded. a little long is better than short. Install the hammer spring screw and keep it tight from now on. Some primers are harder to set off than others.

Smooth is way better than just light. Reliable is better than anything else.

After spending some of my earlier revolver days chasing the perfect trigger I figured something out.

It is much better to learn to be a great trigger puller than to try to get a perfect trigger.