Starting an MPA program in January, what should I know?

For background I'm 22 with a B.S. in Economics and am a current MBA student. I've lost the passion to pursue a business related career a while ago (admittedly even before I started my MBA) and have always had a passion for politics and working in the public sector. I'm switching programs next semester (same school, online), and will likely have two classes transfer from my MBA to MPA to count as electives.

What should I know before starting an MPA? What should I do now to help secure myself a job in the public sector? Which jobs should I start looking for? Any advice is welcomed. TYIA.