Try this:
Place a dime on the flat area right behind the front site. Now site in on a spot on the wall and begin dry firing. The goal is to keep the dime on top of the slide. If it's falling off after a couple of pulls you need to adjust the way you are holding the gun, as well as the way you push the trigger. Lot's of folks like to say pull the trigger, but you should practice pushing it straight to the rear. Yukon said it right, you probably have too much finger on the trigger. When teaching folks to shoot pistols, I always tell them to place the center of the first pad on the trigger, this gives you plenty of flexible areas, ei. three joints, to move while pushing the trigger to the rear. Too much finger, you pull right, too little, you push left. Try the dry firing with the dime, it shows a lot of folks how much they are jerking the trigger. I'm used to my 1911 trigger also, and this M&P trigger took some getting used to, but now I have it mastered. Good luck.
Bill
NRA Life Member
US Marine 11 Years and running
Marine Corps Rifle and Pistol Marksmanship instructor
Expert Rifle and Pistol shooter