Don't think there is much of a step to step thing to add. The village had some problems with only a few villagers left, so I built a wall to protect them, and a big house in the middle with 16 beds, and after that, they started going crazy on overpopulating. I have counted, and there is a total of 24 beds in the village, and I am pretty sure it is more than 24 villagers. Might have something to do with it being often loaded as my house is nearby, as you can see on one of the screenshots.

Edit: I found out something else. If I traded with one villager until I lock the trade, and I go to another in that village of same profession, he would often have the same trades, and the trade I just locked out with the other village, is locked for him too, even though I haven't traded with him for a long while.