What do you do after you beat all 8 gyms in emerald?

After beating all 8 Gyms in Pokémon Emerald you need to make your way to Ever Grande City. To access Ever Grande City you need the Waterfall HM. After making it to Ever Grande City you now need to make your way through Victory Road. To challenge the Elite Four, you will need the HMs Strength, Surf and Rock Smash. To make it through the cave, Flash and Waterfall are not needed but will help you go through the cave.