The basic idea behind different formations is this.... you want as many of your troops firing on your target as possible. Avoid at all costs getting your troops stuck behind each other, especially archers as this means only the front row will fire and you will not be dealing enough damage.
Also make sure if you are sending large layers of pikemen and swordsmen to leave enough room for your archers at the back to fire.
Defeating Small Castles - 4 Side Assault
The easiest most effective way to defeat small enemy castle is a 4 pronged assault. The reason being nearly every troop will fire as soon as the battle starts meaning you will get the maximum attack value during the battle. As you move further into the white line area your troops will cluster together and form a circle of death pretty much firing none stop at everything within the white line area.
For areas that have more archers than other you can thicken up with 2 or 3 layers of archers. It takes 212 archers to fill the 4 sides of the white line with 1 row of archers so attacking with much larger groups of archers such as 500 means you can have double rows or triple rows on multiple sides.
You can also include pikemen or swordsmen in the first layer beside the white line and place the archers behind so neither unit obstruct the other.
Clearing Archers in Towers
The biggest problem you are going to run into when attacking players and AI castle is archer towers. Catapults die too quickly to do enough damage if there are towers filled with archers on the white line as they will target and kill your catapult no matter where you place them. The basic idea is to clear these towers so you can send catapult waves that won’t get targeted by the enemy archers.
You need to place your groups of archer’s right beside the enemy archer towers so as soon as the battle starts every one of your archers will fire at the tower they are beside. It’s no use placing them away from the towers and letting them march at the tower as number one, the will get fired on before they can fire back and two, only the front row of your archers will target the tower meaning they will deal very small amounts of damage before dying. While placing your archers this close to the enemy towers means the towers further in can also hit your archers it doesn't really matter as you will have so many archers firing you will clear a lot of the enemy troops.
Another important thing is to place a few pikemen wherever the sally forth will come from. This will hold it up while the archers fire on it. The sally forth can plough through archers very quickly but when it is blocked a few pikemen it gives the extra few seconds needed to kill it before it can get to your archers. Also use pikemen to trigger killing pits before your archers kill the enemy archers in towers and advance further.
Formations for Wolf Lairs
Attacking large wolf lairs with only archers is a very bad idea. In small groups wolves don’t present a huge threat to your archers because a large group of archers can fire on multiple wolves and kill them quickly. However in very large numbers, 400+ a large group of wolves can charge you and reach your archers killing large numbers of them before you can kill them all. Because archer defence is very low a swarm of wolves can quickly eat through your archers like they are not there.
For Medium sized Wolf Lairs
A simple way to stop wolves targeting your archers is to distract them with a small number of pikemen spaced out before your archers.
A group of wolves should swarm each of them and your archers can fire on them and kill them before they reach your archers. You will lose the pikemen but it’s a small price to pay. Only use this method if you are low of pikemen. Preferably use the method for large wolf lairs below for every wolf lair if you can.
For Large Wolf Lairs
This is the most effective way I have found to take down the biggest wolf lairs with 400+ wolves. the losses vary from 5 to 20 pikemen lost which is a very small number and you will lose no archers in these attacks.
150 pikemen and 250 archers is what you need. Just fill a vassal and you can attack multiple large wolf lairs with this number. You can have slightly below this number as all you really need is a very large group of pikemen and archers and proper positioning at the start of the battle.
Place your block of troops directly on the white line on the side with the biggest amount of wolves. Place 3 lines of 50 pikemen and 6 rows of 50 archers. Because pikemen have very high defence what you want to happen is you want as many wolves as possible to swarm your large group of pikemen. What will happen is a lot of the wolves will become trapped behind the other wolves in front meaning they cannot attack. Only the wolves at the front will and they will cause very minor damage to your pikemen. In the meantime your archers will be firing like mad at the wolves killing them like flies. At the start you should have eliminated most of the wolf lair before you troops even march much into the white line area and the remaining wolves will be picked off by you advancing pikemen and archers.