## Yes you can. ##

The Ready action is what you're looking for. It's explained on p.192 of the player's handbook.

> First, you decide what perceivable circumstance will trigger your reaction.

For you this would be, "If anything nasty comes towards me"

> Then, you choose the action you will take in response to that trigger, **or you choose to move up to your speed in response to it.** 

So your response would be, "I run in the opposite direction!"

So you use your action Ready to run and then, when a monster approaches you, you may use your reaction to move away. Generally you won't also be able to also Dash since that would require another action.