The first thing that starts to change him is he starts to read books. When Montag realizes he is unhappy because of the things happening in his life, he wonders if books hold the answer. He thinks that since Mrs. Blake was willing to die for books that there is something to it.
The next thing that helps him change is starts to care about things. He cares about Clarisse and she is one of the reasons he changed. She was the one that helped him realize his unhappiness in the first place. He starts to actually care about