My M&P9c has a fairly smooth trigger pull of 6.2 pounds and I put a touch of Tetra gun grease on the contact points between the trigger bar, sear and striker block and also between the sear and striker and now my trigger pull is at 5 pounds. I can't believe just a little grease could make that much difference, but it did.
Of course I'll clean and re-grease after every range trip.