

Try not to focus on one type one one Pokémon.Try to get a counter for each type (you can look up on effectiveness tables like this (German) to see which one counters).In 6th generation, story mode has been made even more easier. So if you can't beat on first time, just level 5 levels further and you go. As you have endless tries to defeat opponent trainers, you are also able to train your Pokémon to oblivion.

Since the first Pokémon games (Red/Blue/Green) gameplay mechanics were really simple. Sorry to give you that answer, but: It doesn't matter!
