Where do I begin solving my multiplayer game's lag?

I’m working on an arena based multiplayer space combat game, and unfortunately clients have a ton of lag making it difficult for them to compete against the listen server host. Naturally the host will have some sort of latency advantage but it’s borderline impossible for a client to beat the host in a 1v1 engagement because ship movement is so choppy on their end.

This is my first ever multiplayer project so I’ve got no idea where to even begin fixing the lag. Can someone point me in the right direction? Like a video tutorial or even some documentation to study.