How to add recoil to this script?

this is my script and i dont know much about vectors so i cant figure out how to add recoil.

public var MoveAmount : float = 1;

public var MoveSpeed : float = 2;

public var GUN: GameObject;

public var MoveOnX : float;

public var MoveOnY : float;

public var DefaultPos : Vector3;

public var NewGunPos : Vector3;

  function Start(){
 

DefaultPos = transform.localposition;

  }            
  function Update () {
 
 
  MoveOnX = Input.GetAxis("Mouse X") * Time.deltaTime * MoveAmount;
          
  MoveOnY = Input.GetAxis("Mouse Y") * Time.deltaTime * MoveAmount;
      
  NewGunPos = new Vector3 (DefaultPos.x+MoveOnX, DefaultPos.y+MoveOnY, DefaultPos.z);
  
  GUN.transform.localPosition = Vector3.Lerp(GUN.transform.localPosition, NewGunPos, MoveSpeed*Time.deltaTime);
  
  if(Input.GetMouseButton(0))
    DefaultPos = -1;
    yield WaitForSeconds (2);
    DefaultPos = 0;
 
   }