Cheat mode
Note: This procedure involves editing a game file; create a backup copy of the file before proceeding. To edit stats of your skirmish player, use a text editor to edit the "[player name]skirmishstats.ini" file in the "c:\documents and settings\[user name]\application data\my battle for middle-earth files" directory and edit it accordingly.

More powerful creatures
To make a Troll more powerful, have it pick up a tree as a club. It is slower, but much more powerful. To make an Ent more powerful, have it to pull boulders out of buildings or rock piles to throw at enemies. This is a very powerful long-range attack.

Good army spying in skirmish mode
The Evil factions of the game both have a Spying power they can use. However, Good factions have no spying power. Early in Skirmish mode, recruit the Hobbit available to you. Have him run over to an enemy castle, camp, etc. He should be able to make it to the citadel, unless the enemy is playing a Good faction and has closed the castle gate. Once inside (or outside the gate if it has been closed), activate his Elven Cloak. He will remain there, untouchable by the enemy. By doing this, you will have a permanent spy. Note: If he moves, he will be exposed until he can use his cloak again. When selecting all your units by pressing Q, hold [Shift] and deselect your spy before ordering everybody to move or attack.

Bypassing the command point limit
If you have reached your command point limit during a mission, send out a battalion or two (with the Banner Carrier upgrade) of soldiers. Have them fight until there is only one or two men remaining in the battalions/hordes. Then, send them back to your base, near a Healing Well for the Good side. You have just freed up several command points. Your damaged battalions can regenerate. Use this strategy to make up to three battalions of cavalry to raid your opponent with.

General strategies
Hordes/Battalions with a Banner unit should be retreated when only a few remain to allow the ranked unit to regenerate.

Always close your Castle Gate and build a Postern Gate instead.

Try to grab as many of the economy/outpost plots surrounding your base.

Fewer upgraded units are always better than many non-upgraded units.

Build two economy structures per one unit production building.

Build economy structures in the back of the Camp/Castle and build unit production structures in the front.

Small cavalry is better than a large infantry, except against archers.

Do not blindly put any group of soldiers against any enemy soldiers. If you have cavalry, make sure to have archers as back-up against pikemen and the like.

In skirmishes, build a wide variety of hordes, but mainly use Archers and Monsters above Foot Soldiers. Always have all Heroes before an attack. Keep gates closed and heavily guarded. When all allies are defeated, use specials to summon units like Summon Ent Allies or Rohirum Allies. When raided, build as many Orc, Oruk, Gondor, and Rohan archers as possible. When you are outnumbered and other units that you control are far away, run away.

source: http://www.cheatcc.com