Are there “rules” to playing online?

I’ve always loved watching competitive AoE2 on YouTube and I wanna try getting into it. However I’m god awful at the game (can’t beat most of the campaign missions beyond the first 1 or 2) and I’ve never played online so I don’t know the quote/unquote rules of playing online. I also get kicked from lobbies a lot so I’m assuming there’s something I’m not doing right when I join. I know some people have public lobby’s that should actually be private so I try to just join the ones with “all welcome” and such in the title