Julius03

I have played KSP for quite a while and now I’m trying to design a reuseable two staged rocket. Kind of like SpaceX’s Starship. I just don’t know how I could determine the size ratio between the two stages to make it as efficient as possible. Should the 1st stage be 4 times bigger than the 2nd stage? 3 times? What I’m really asking is if there’s an easy way of determining this or should I just experiment like always? Maybe adding more engines or having it refueled in orbit more instead?