I'm currently reading Robert L. Heilbroner's "The Worldly Philosophers" which gives an outline of the basic ideas behind the thinking of Smith, Marx, Mill, Keynes etc… Though I have found it fascinating it is slightly muddied by Heilbroner's biases, as the works of Hayek, Friedman, Rothbard and others are entirely ignored or only given passing reference. Otherwise though, it gives a great beginners guide to the ideas of several pivotal figures.

I just took a class on International Political Economy and the textbook we used was Thomas Oatley's International Political Economy which struck me as readable and pretty approachable for beginners. It is not, however, a theoretical or philosophical discussion of political economy.

I'm also currently reading A Political Economy of the Middle East but I am not sure I would recommend it unless you had had some intermediate econ courses at least.

/r/asksocialscience might be a better place to ask. That being said, I can suggest a text: "Theories of Political Economy" by Caporaso & Levine. It seemed like a solid primer when I TA'd an intro course last year, and it's fairly concise. However, it is old and there may be better alternatives.

Any background in political philosophy, political science, or basic micro- and macro- economics will help a lot. Depending on your focus, I'd add international relations to that list.

Historical literacy is also a must. As with any field, there's some intellectual history to consider, and this is particularly true of political economy.

My wife actually published a fairly accessible textbook on Political Economy which is pitched at the introductory college level.

There's plenty of used copies out there and there's been no need for a second edition so, if you're interested I'd pick it up used; I certainly can't see any reason you'd want to throw down $70+ for it.

Muller, Adam Smith in His Time and Ours

John, ed., Ruling Passions

Seconding The Worldly Philosophers, as well as adding The Theory of Capitalist Development by Paul Sweezy, and The Theory of Monopoly Capital by Paul Sweezy and Paul Baran.