You will need the following TM's to do this.
1. rock smash
2. surf
3. fly

Battle gaby and dat camera man till their pokemon reach lv 39(max lv for their pokemon)
Then place 1 strong pokemon in front and 1 weak pokemon as the partner. Then make the strong pokemon hold the amulet coin and make the weak pokemon hold the exp share. If u win u get about 7k each battle but i 4got how much exp dey earn. bout more dan 2k exp. good for trainin weak pokemon. keep goin onto their spawn points

1) route above maville city or w/e u call it
2) route at the right of mauville city
3) route at the right of fortree city

keep doin dis and ull b rich with strong pokemon in no time