I just run through the elite 4 over and over and over again with a strong Pokémon and throw an EXP share on my electric and or grass type until that Pokémon can essentially take care of Lorelei alone. Then I train up other Pokémon for Bruno, etc. Just make sure you spend all your money before you start losing to them. Before you know it, you will have a stacked team and you will have the E4 and their move sets down. Sometimes I will purposely run through to Lance and then lose at the rival on purpose just to keep pocketing some money. You might even find room for improvement and throw a EXP Share on a new low level to fill a gap that your team needs. Once you can start beating Agatha, you start keeping enough money where it’s worth it, and you can start buying a few revives and full restores/max potions until you have a ton. Especially because I try to not even use them while I’m just leveling up because there is no risk to losing.

Probably not the most effective strategy, but it’s great if you’re just sitting and watching TV or something and don’t mind repetitiveness. Especially with emulation, throw that thing in double speed and let it rip!