Like others stoning/polishing the rebound slide, spring hole in rebound slide and a lighter rebound slide spring help DA trigger a great deal. Fill it with snap caps, practice pulling the trigger DA as fast as you can until you can go 50 or 100 pulls rapidly without stopping. This will polish the moving parts and develop your hand strength for DA firing. I don't normally change out or reduce main springs. polishing the mainspring strut might also help a little.