How can I build a competitive application for a PhD?
The American Economics Association has compiled a list of professors’ blog entries and departmental advice pages on the topic of pursuing a PhD in Economics: https://www.aeaweb.org/resources/students/grad-prep/considerations  

One you might find especially useful is Chris Blattman’s, whose work is at the intersection of politics and economics: https://chrisblattman.com/about/contact/gradschool/