While Bradbury doesn't go into the details, it seems clear this society is controlled by a small ruling cartel that has decided what is best for everyone. A guiding principle of this society is that too much thinking leads to unhappiness. As Beatty, who mouths the orthodox ruling class opinions in the novel states:
Don't give them any slippery stuff like philosophy or sociology to tie things up with. That way lies melancholy. Any man who can take a TV wall apart and put it back together again, and most men can nowadays, is happier than any man who tries to slide-rule, measure, and equate the universe, which just won't be measured or equated without making man feel bestial and lonely. I know, I've tried it; to hell with it. So bring on your clubs and parties, your acrobats and magicians, your dare-devils, jet cars, motorcycle helicopters, your sex and heroin, more of everything to do with automatic reflex . . .
Control comes from discouraging any critical thought or genuine mental exercise. People are all supposed to act like everyone else and enjoy the activities that society dictates are enjoyable. People like Clarisse, who prefer conversations, observing nature, and taking walks rather than watching the TV walls, are considered social deviants. Social non-conformity, rather than being seen as healthy, is stomped out as far as possible. Reading, of course, is illegal.
While mindless amusements are supposed to keep people happy, we see that, in fact, such a life leads to misery. Mildred tries to kill herself, and Montag wakes up from a stupor of dull unhappiness when he meets Clarisse and realizes how vacant his life has become.