First order of business is to determine which S&W model pistol you have.
Some pictures would be useful, of the light firing pin strikes.
Light firing pin strikes can be caused by a number things, including: hardened oil or grease in the firing pin channel, slide failing to go fully into battery (firing position), damaged firing pin tip, kinked or broken firing pin spring, excessive headspace, and so on. We need more details to narrow it down.
As a general rule, a detailed disassembly and thorough cleaning and lubrication is in order. Refer to the archives for detailed dissassembly diagrams and instructions. If you are not experienced at this, it would be best to take it to a gunsmith for servicing.