Missions throughout the game

Mostly in the game there will be missions.The most hardest mission in the game is going to Sunyshore city.You first will need to defeat Candice the 7th gym leader in Snowpoint city then go back to Veilstone to the galactic building talk to the galactic grunt then when he runs away get the poke ball that was under him.Go inside the building and free the trio of pokemon.then go to the Oreburgh cave side and go to the peak and battle Palkia.

How to pick good Pokemon

To pick good pokemon always pick the strongest.You also should pick a variety of different types of pokemon (psychic,electric,grass,normal,flying,snow,dark,rock
,water and fire.)

You will need different types throughout the game.