Mid game villager assignment tips?

I find my eco is usually quite balanced from dark age to late feudal, and in post imp games, but I find that I always end up abusing the market in order to balance my eco at around castle age to early imp. I think assign my villagers poorly and usually end up at some sort of eco imbalance

Does anyone have any tips on this? Is it just eye balling it and "feeling" it from practice or do you guys have some quick maths you do on the fly (like, lets say you know how many vills you need to sustain 2 stable knights, so you just add or subtract from that number if you're doing something else)