Attach this Script to any UI Element on your Canvas to make it self auto selected when it get's enabled. Useful for Gamepad only games!

UIAutoSelectSelf.cs

using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;
using System.Collections;

[AddComponentMenu("Helpers/UI/Self Auto Selected")]
[RequireComponent(typeof(Selectable))]
public class UIAutoSelectSelf : MonoBehaviour
{
    public bool AutoSelectOnEnable = true;

    private EventSystem _sceneEventSystem;

    void Awake()
    {
        _sceneEventSystem = FindObjectOfType<EventSystem>();
    }

    void OnEnable()
    {
        if(AutoSelectOnEnable && _sceneEventSystem)
            StartCoroutine(DelayedSelfSelect());
    }

    IEnumerator DelayedSelfSelect()
    {
        _sceneEventSystem.SetSelectedGameObject(null, new BaseEventData(EventSystem.current));
        yield return null;
        _sceneEventSystem.SetSelectedGameObject(this.gameObject, new BaseEventData(EventSystem.current));
    }
}