Domain Knowledge

When it comes to domain knowledge of politics, you probably either know it or you don’t. If you’ve ever worked in progressive politics before, then you’re fine. If not, you can’t really learn it anyway.
But you can try. Pick up the The Victory Lab by Sasha Issenberg, and read Patrick Ruffini’s excellent breakdown of the 2012 Obama for America Analytics team.
Most importantly, try to volunteer for a local campaign doing literally anything.