Welcome! I was all over the place with my introduction to King, but if I had to pick a starting point from what I've read, it would probably be either Revival or Joyland. I'm sure a lot of people would suggest otherwise, but both are nice consumable stories that give you a sort of concentrated dose of the King flavor, and based on what I've read so far, I think both indicate how much he has developed (even though critics seem to disagree).
If you have any suggestions or notes about how and when to start Dark Tower, I'd be grateful, I loved The Eyes of the Dragon intensely, but otherwise I have zero experience with fantasy. I trust King, but I also know I need to be ready to really appreciate what he's putting out there. Either way, welcome!