Go back to petalburg and battle your dad
After you beat leader Norman
Beat the gym leader
get better pokemon
get a pokemon, then you train it, get it really strong, and beat th ecrap out of all the 7th leader's pokemon. Its easy.
you get a dark Pokemon for example mightyena
with fighting type pokemon
You beat Leader Norman, then someone gives you surf.
Water, dark and grass Pokemon
in the fortree city
keep using phychic
Back to Petalburg, to battle the fifth Gym Leader.... Your Father. (da-da-dun...)
you go to the elite four and defeat them.