// file: WaypointManager.cs
using UnityEngine;
using System.Collections;

public class WaypointManager : MonoBehaviour {
  public GameObject[] waypoints;

  public GameObject NextWaypoint(GameObject current){
    if( waypoints.Length < 1)
      print ("ERROR - no waypoints have been added to array!");

    // default is first in the array
    int nextIndex = 0;
    
    // find array index of given waypoint
    int currentIndex = -1;
    for(int i = 0; i < waypoints.Length; i++){
      if( current == waypoints[i] )
        currentIndex = i;
    }
    
    int lastIndex = (waypoints.Length - 1);
    if(currentIndex > -1 && currentIndex < lastIndex)
      nextIndex = currentIndex + 1;

    return waypoints[nextIndex];
  }
}

// file: MoveTowardsWaypoint.cs
using UnityEngine;
using System.Collections;

public class MoveTowardsWaypoint : MonoBehaviour {
  public const float ARRIVE_DISTANCE = 3f;
  public float speed = 5.0F;
  private GameObject targetGO;
  private WaypointManager waypointManager;

  private void Awake(){
    waypointManager = GetComponent<WaypointManager>();
    targetGO = waypointManager.NextWaypoint(null);
  }

  private void Update () {
    transform.LookAt( targetGO.transform );
    float distance = speed * Time.deltaTime;
    Vector3 source = transform.position;
    Vector3 target = targetGO.transform.position;
    transform.position = Vector3.MoveTowards(source, target, distance);

    if( Vector3.Distance( source, target) < ARRIVE_DISTANCE)
      targetGO = waypointManager.NextWaypoint( targetGO );
  }
}