I'll tell you what I think you can avoid completely:
Tommyknockers
Rose Madder
Dreamcatcher
Insomnia
Liseys Story
Everyone has opinions obviously but those are, to me, some of the bottom of his barrell. Like other have said King shines when he's working in short form. Short stories, novellas, etc. Pick up any collection and you'll find gems. Some of his best short work is The Jaunt, Graveyard Shift, In the Death Room, 1408 and many others. His novellas often receive some of his highest praise. The Mist is is arguably his most popular short story/novella. 1922 is one of the bleakest, darkest things you'll ever read. Four Past Midnight has 4 good to great novellas, The Langoliers and The Sun Dog being the best ones, imo. Langoliers is basically one of the best episodes of Twilight Zone never made. Night Shift was his first collection of short stories and has some great nightmare fuel. He was shooting out almost constantly great horror back then.
One of the cool things about getting into King is that his reputation is a horror writer, but you start reading his work and you see that he's far more than that and has a great range of genres. The Stand is, imo, a modern classic. Misery, The Dead Zone, Salems Lot, The Shining and Carrie are all some of his early works that are still held in high regard. Now, in his old age, I think he's actually hit a nice stride in his storytelling and has even managed to not fumble the ball towards the end. 11/2/63, Revival and The Outsider are all good reads where the ending doesnt seem like it fell off the rails.