To me there are a few details that stand out as elements of foreshadowing after I have read the entirety of the story.
First, the stones that the children were playing with in the beginning seemed so simple and purposeless. By the time the resolution of the story is complete, I know their purpose.
Second, the fact that Tessie Hutchison is late always made me wonder until I get to the very end. Of all the people, why is she late? I wonder, would it have had as great an impact if a different person were late? Probably not.
Third, the references of the old man who suggests that the lottery has to be done because it has always been done makes me think evil. It makes me think of the things in our society we do just to do them, not so much that they are right. This makes me wonder what the great evil is going to be in the end.