How can I build a competitive application for a PhD? Thank you all in advance!

I have the intention to apply for a PhD within the next year to start in Fall 2019.

I have an undergraduate degree in Finance and was selected best finance student of the university upon graduation. On top of that, I was a student-athlete on a soccer scholarship and made it to the all conference academic team each and every year, finishing my degree with a 3.74 GPA. 

After that, I completed a MBA from a AACSB accredited school as graduate assistant for the department of Finance. Apart from working in the finance department, I also worked in a research center for Sport security, mainly doing analysis more than research. 

Now, I have been working for 1 year as an operations specialist for a financial insititution. My first question is, does this make me a competeitive individual for a PhD? I was thinking of doing it in Politics, Political economy, or economics. Is there anything else I can do during this next year to make my candidacy Stronger? What kind of jobs can I look for to get that extra experience? Where could I publish my own article or my own work to add it to my candidacy? 

On another note, one of the requirements to apply is to submit writing sample, is it possible to send some article of publication of my own, or should I send something I wrote in school? 

Currently, I am working on my GRE examen to make sure I am in at least the 90th percentile.

Sorry for the length of the question, but I wanted to give a clear overview of my Situation. 

Thank you very much.
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/