Like any creator that has a huge body of work, there are gonna be hits and misses. I haven't read much of his older stuff, but I'm currently reading 'Salems Lot. I wouldn't say it's knocked me over, but I am enjoying it.
I have also read the Shining and Dr. Sleep and I enjoyed those immensely. Of his more recent stuff, I really like the Holly Gibney character and her arc in various novels and short stories.
You can start with "If it Bleeds", it's an anthology of short stories, the last of which is a Holly Gibney story.
I didn't care for "Sleeping Beauties", which he co-authored with his son Owen.