@DontTread thats a big question because I am not clear what you desire. Are you talking about at deity/immortal level?
At these levels you need to understand that the AI civs have huge bonuses and to catch up with their science/culture climb you have to grow fast amd with agressive barbs you need a good starting army and it just makes sense and to a degree a necessity to take out anything close to you after this or you will seriously struggle.
At lower levels it is not that hard to win so it is about what you mean by plateau... Not winning fast enough? Not playing enough variety?
I play about 20% deity, 40% emporer and 40% prince. Of the three I find prince the most pleasurable playing different games. One of the best lately was seeing how many envoys I could create.
Emporer is a great challenge as I like to win without initiating a war and deity because many discussions are at this level
I am an OK player but not brilliant in comparison to what people post but always keep in mind that not every game played goes as well as those posted. I think the biggest tips are reading the GOTM games and certain people like
@elitetroops post some very inciteful tips.
My best tip lately is the word you use... Focus. The first 100 turns it is easy to go off track and staying focused on the primary goals really helps, especially building certain districts quickly.
After 100 it is easy just to click next but there can be a lot of things like card changing I often loose focus on. Keeping focus seems to significantly increase my play
Try a prince game focusing solely on getting 100 envoys. Its not easy.