Preparations

Getting an administrator (senator, chief, chieftain, logades, nomarch):
In order to get an administrator you need to research him in your academy level 20 (you also need a rally point level 5 as Teuton or level 10 as Gaul, Roman, Egyptian or Hun). 
You must also have your palace or residence to the correct level. A residence can train three settlers or one administrator at level 10 and 20. A palace can train three settlers or one administrator at level 10, 15 and 20.
After this you can train him in your palace or residence as long as you have a one or more free expansion slots.

• The Senator (Roman) is very eloquent and persuasive; he can lower the loyalty by 20% to 30% each time.
• The Chief (Teuton) is especially cheap; he can lower the loyalty by 20 to 25%.
• The Chieftain (Gauls) is 25% faster than the others; he can lower the loyalty by 20% to 25%.
• The Logades (Huns) is as cheap as the Chief and can surprise; he lowers the loyalty by a value between 15% and 30%.
• The Nomarch (Egyptian) is most expensive; he can lower the loyalty by 20% to 25%.

These values for the administrators are for the optimum case, due to the morale bonus they will most likely not be like this when taking over a village. After the loyalty reaches 0% the administrator who did this will vanish and the troops guarding him will stay in the village as defence.

Attack

Conquerable villages:
Only villages that are not the capital of a player can be conquered, regardless of where the palace is.

Hint: You can only conquer a village when the residence or palace is destroyed, you have enough culture points, the village you are attacking is not the capital and not the player's only village.

Attack waves:
The conquering should consist of waves because sending everything in only one attack is very foolish. The first wave should be the one with the "cleaner" which kills all defenders, afterwards the catapults destroying the residence or palace followed by the administrators.
Assuming that you own 3000 Imperians, 60 catapults and 2 Senators:

1. 2700 Imperians should be sent as a normal attack to avoid trouble ("cleaner").
2. 150 Imperians and some catapults should be sent to destroy the residence or palace. This should be a normal attack or the catapults won't shoot!
3. 150 Imperians and some Senators should be sent. This should be a normal attack or the Senator won't do his job.

Repeat steps 1 through 3 as often as needed to check whether the victim rebuilt his residence or palace!

Hint: All tribe specific buildings (e.g. city wall, trapper or brewery) will get destroyed after a successful conquer of another player and have to be rebuilt. Furthermore conquering a village of a smaller account will lead to a decrease of 1 level for each building. However if you conquer your own village no building or building levels will disappear.
Any villages settled or conquered by the newly conquered village will continue to occupy the build slots in the newly conquered village. 

After the attacks

Rebuild the residence or palace as fast as possible to raise the loyalty again and put some decent defenders including some spies into the village. The loyalty of a village rises by 2/3 of a level of the palace or residence per hour. For example, a level 6 residence or palace will raise the loyalty by 4 points in one hour.

When a village is conquered, all troops that belong to the conquered village will disappear. This includes troops belonging to the conquered village that are currently out of the village (troops that are reinforcing other villages or on their way to/from a destination). Furthermore any researches made in the conquered village are reset and the wall surrounding the village will disappear. Finally any tribe specific buildings, such as the horse drinking trough, will also vanish when a village is conquered. All of this applies even when you are conquering your own villages.

Game Restrictions

The restrictions limiting conquering you can find here.