If you're not into formal theory, then I'd recommend taking a "Mathematics for Economists" course if your school offers one. Such a course emphasizes math literacy over proofs and covers a range of topics that span basic calculus to differential equations. Check out the book by Simon and Blume (http://www.amazon.co...n/dp/0393957330) -- you could read a chapter a day and finish the book in a month. Additionally, you should also take a course in game theory. These courses should suffice for comprehending the arguments presented in formal models in journal articles.