I always focus on battle winners.
Battle winners = cards that end the battle in your favor.
This could include: choose the blocker/rescuer, capture, discard, remove from game, conversion, etc.
Next, I focus on drawing and search cards to get to the battle winners.
Third, I look for heroes/evil characters that have good abilities to get to the battle winners or guard from them with protection.
My ratio is 1:1, character to enhancement, at the most.
I fill in Arts and Sites as they fit my strategy and/or need.