I created a simple game in which the player collides with the enemy, and the score will increase by one. How to do it correctly?

Below is my code:

```
public class Bird : MonoBehaviour {
    public GameObject deathparticales;
    public Vector2 velocity = new Vector2(-2, 0);
    public float range = 5;
    public int score;
    private string scoreText;

    // Use this for initialization
    void Start()
    {
        score = 0;
        rigidbody2D.velocity = velocity;
        transform.position = new Vector3(transform.position.x, transform.position.y - range * Random.value, transform.position.z);
    }

    // Update is called once per frame
    void Update () { 
        // Die by being off screen
        Vector2 screenPosition = Camera.main.WorldToScreenPoint(transform.position);
        if (screenPosition.x < -10)
        {
            Die();
        }
        scoreText = "Score: " + score.ToString();
    }

    void OnGUI () 
    {
        GUI.color = Color.black;
        GUILayout.Label(scoreText);
    }

    // Die by collision
    void OnCollisionEnter2D(Collision2D death)
    {
        if(death.transform.tag == "Playercollision")
        {
            score++;
            Destroy(gameObject);
            Instantiate(deathparticales,transform.position,Quaternion.identity);
        }
    }

    void Die()
    {
        Application.LoadLevel(Application.loadedLevel);
    }
}

```