[llamabeast]

In order to get an advantage against the AI, you need to concentrate on magic.

Firstly, make sure you recruit a sauromancer every single turn. Put them on research.

You want to head straight for "Raise Skeletons", in Enchantment (Enchantment 3 perhaps?). Then your sauromancers will be able to help you a lot in battle by producing vast hordes of skeletons.

Also, research evocation for "Shadow Blast". It costs a gem, but it's viciously powerful.

As Torin says, Darkness is a very powerful spell, which will help you a lot, although it will take a while to research.

If you have spare death gems, Pale Riders (Enchantment again) will give you large numbers of cavalry quite cheaply.

Hope that helps! If you manage to make really good use of magic, you should be able to kill a great many AI troops for every one that you lose. Then you can save some money for a second fort (might be a good idea to prioritise that quite highly), and so on.