Just a few more thoughts:
1. You can channel more funds into happiness with the slider on the domestic Adviser screen, even 10% provides a 'Brave New World' (excuse allusions to Aldus Huxley).
2. Change your system of government if you've been at war for too long. I usually stick to Monarchy, as monarchists are more forgiving of my war-mongering. Communism is handy, too. If you're fighting a long war under Democracy or Republic, your citizens will get steamed up and your cities will start to smoke. If you're a religious civ, it's easy to swop around; if not pick the government that suits you and stick to it.
3. Having a Wonder such as Sistine Chapel will make your Cathedrals more happiness-producing. There are several others, and you will learn which are your personal favourites.