Games : Civilization 5 tactics for Prince difficulty and beyond

I was new to the series when I first purchased this game a few months ago(with the Brave New World expansion pack), but after playing the first 3 difficulty modes I got a good hang of the game. However, when I tried playing on the Prince difficultly level, I was brutally defeated. Within a few turns after starting the game, I had civilizations declaring war on me. If I concentrated on military development, then the happiness of my empire plummeted and I experienced a shortage of workers and resources. A non-militaristic focus got me mauled by my unfriendly neighbours in another attempt. What is the best way in which I can be up and running here? I could barely make it past the first 80 turns.