var thisObject : Transform;
var Player : GameObject;
var speed : float;

function Start(){
thisObject = transform;
Player = GameObject.FindGameObjectWithTag("Player"); // Или Player = GameObject.Find("Player");
}

function Update(){
var pos : Vector3 = Player.transform.position;
pos.y = transform.position.y;
transform.LookAt(pos);
transform.position += thisObject.forward * speed * Time.deltaTime;
}

Vector3 hit = Vector3.zero;
  if (Input.GetButtonDown("Fire1"))
{
       Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
       RaycastHit rhit;
       if (Physics.Raycast(ray, rhit))
       {
             if(rhit.collider.tag == "Terrain") hit = rhit.point;
        }
}

using UnityEngine;
using System.Collections;

public class Moveunit : MonoBehaviour  
{
  void Update ()  
  {
   Vector3 hit = Vector3.zero;  
     if (Input.GetButtonDown("Fire1"))  
    {  
         Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);  
          RaycastHit rhit;  
          if (Physics.Raycast(ray, rhit))  
          {  
               if(rhit.collider.tag == "Terrain") hit = rhit.point;  
           }  
    }
  }
}

if(speed >= 30){
speed = 30;
}