So you're a ranged combatant riding a controlled mount, maybe a horse. Regarding "Controlling a Mount", the PHB states about controlled mounts:
It moves as you direct it, and it has only three action options: Dash, Disengage, and Dodge. (PHB, p. 198)
Can you direct the mount to ready the Dash action (maybe on the trigger "whenever an enemy comes within 10 ft. of us, move away"), or is this prohibited by RAW since Ready is its own action?
Additional: As a DM, would you allow it, or would this make your job of challenging the players too difficult?