First, heres some tutorials.

1. when you use rain dance, thunder wont miss
2. with the arcade star's zapdos, sent out a pokemon with the ability mold breaker, it will be weak against any ground type moves!!!
3. use sunny day before using solarbeam
4. DO NOT have moves of the same type, unless it is a move like rain dance or calm mind.
5.try to use pokemon of All different types of pokemon, it is most efective.
6. using pokemon that can cover your other pokemon's weakness' is a master technique that all pokemon trainers use
example:grass,water,fire

using those tips, heres some pokemon that i use

latios
moves: dragon claw, thunder, rain dance, psychic

weavile
moves: sword dance, night slash, ice punch, brick break

garchomp
moves: draco meteor, earthquake, brick break, flamethrower

electivire
moves: thunderbolt, ice punch, cross chop, earthquake

blazicken
moves: sky uppercut, thunderpunch, night slash, blaze kick

swampert
moves: earthquake, body slam, water pulse, ice punch

note: to teach swampert body slam, you must teach it the move in battle frontier on pokemon emerald before migrating


hope this helps!!!