lol one time I accidentally went to the Elite Four before I was prepared but I had tons of revives because that was basically what I only ever spent my pokes on and I just kept reviving until they killed theirselves with struggle =b1. Bring Pokemon that are at around level 70.
2. Bring lots of revives, hyper potions, full restores, and MooMoo milk.
And don't forget step 2!