Basically, you can post one of two things...
1) a villager who is soon to be moving out of your village - some one may well want that villager in their village so they'd make a deal with you for him/her. Then the day before the villager moves out, they come to your village, speak to them and they'll agree to move on to the new village
2) a villager who you would like to receive - posting this info for people who have your wanted villager moving out soon in their village is great as it means you're very likely to come across the villagers you want. Some people will ask for bells, items or a different villager in return. It's all about negotiation. You may even be lucky enough to find some one who's willing to give wit villager away for free
Do you have to have open space to get the villager when it is moving? Or will it just "cut in line" and be the next one to move into your town once you have room for them?
Example: I have 10 villagers. I go to a friend's town and talk to their villager who is moving out. Assuming it is possible even though I have 10 villagers, I get the moving villager to agree to come to my town.
Once I have someone move from my town, I should expect the friend's moving villager in mine? (Assuming I didn't try to recruit others)
If I have a villager someone wants, even if it didn't say anything about moving out, would it be negotiable too? Is there a guaranteed, quick, proven method of making villagers move out without TT?