The game has some code for dodge. Modders have already added the rules in.
As for ready an action. One option: at the cost of your reaction you can delay your turn ( go later in the turn order so you let the enemy run up so you can attack them).
More difficult option: use your reaction to set up an attack when an enemy comes into range. You might just pick first enemy to approach or maybe pick a specific enemy. Maybe you pick an area, a cone, and you automatically attack the first enemy that enters that area until your next turn.
