#3 Only heal outside of battle or at Pokemon Centers
This one takes a bit of self control. Using a paralyze heal or awakening to cure an impaired Pokemon is often the easiest way to stave off frustration in the midst of battle. However, using items gives you a rather unfair advantage over your NPC opponents because most won't use them, thus making many battles a walk in the park. Well, gym leaders do heal their Pokemon, but they're the bosses of the Pokemon world and should be allowed an advantage or two over you.
You can take this method to the next level by not using items at all and only healing at Pokemon Centers. This requires even more patience because frequent trips out of caves and back to town can become tedious, but it's also a sure-fire way to make Pokemon X and Y much harder.
