If you don't have any ev trained Pokemon it will be much harder.
If you don't you should try getting Pokemon with a wide range of types.
Next get moves that have good coverage all around and have good pp.
You should look up which kind of Pokemon each of the elite four has.
After you have done that and still cant beat them then you should go and level up
more.
I beat the elite four with my highest Pokemon being at level 53 and my lowest at level
43
Train them till lvl 55 -60.I beat them on lvl 62
You Beat Boom Bot LvL 48 By.................Looking on Youtube.com
It depends on the moves, however a grass type is recommended.
I beat it with staraptor lvl.58 uxie lvl.53 palkia lvl.57 torterra lvl.48 geodude lvl.8 and quagsire lvl.20 with revives and hyper potions
you have to get all 8 badges beat the elite four and a good team example level 40 and up i beat them the with rampardos lvl 41 infernape lvl 56 ambipom lvl 39 magmortar lvl 49 and a lvl 70 crobat
no i could not beat him with lvl 69s but i beat him with a lvl 81
you got to be lvl 12 or 13 or 14 or 15 i was lvl 15 when i beat him
I beat it with Staraptor lvl.57 uxie lvl.53 and palkia lvl. 56with torterra lvl.47 geodudelvl.8 and another weak pokemon(i forgot which one.
you dont
i beat it with lvl 37 and 38
in mt gemma i used lvl 26 pegasoar,lvl 26 duskot ,lvl 26 grimstone and lvl 26 streamsmash
there is a lvl 70 rayquaza only if you DO NOT do the sootopolis gym 1 time cannot do it or it will not be lvl 70 it will be a lvl 45 rayquaza (it will be a lvl 45 if u beat the sootopolis gym u can do it as many times as u want just dont beat the gym or it will be a lvl 45)