Pokémon

I’ll be using gen 4 and below as older since that’s what I’m used to,

I have Platinum and Emerald and I’ve been wanting to play through them to get to the end game to play the battle tower or equivalent since their online servers are shut down (or non existent with the GBA)

I guess I’m just looking for tips and a discussion as to how everyone plays their Pokémon game. I find that whenever I play through any Pokémon game, with the exp. share shared or not, I always over level one Pokémon. Not too much, at least not as bad as when I was a kid, but in my emerald game it got to the point where I had a grovyle in the second gym and my other three Pokémon were level 10 below. How do you maintain a balance? Again, I’m not a new player, I’ve been playing Pokémon for almost all my life and I’m 24, however I’ve always been bad at party management type games and I’ve been wanting your opinions/discussions on this topic.