Early unit types
If you have an item that increases the EXP of a certain
unit category (for example, Arbalest - Archery EXP +30), equip
it on a person with the corresponding unit category. After doing
so, choose a certain unit type with the higher EXP points. After
you have selected one, you can unequip the item, and have the
new class with your basic EXP.
Long distance army swaps
One of the obstacles in the game is having a strong
force on one side of the map while needing that force on the other
side. Since the distance per turn rules bar any army from getting
across the map in one turn, this can lead to a second rate army
having to fight a first rate army. If the two distant armies are
connected by territory (linked to the capital), you can simply
trade one army for another by using the following trick. Choose
"Form" at one army and remove all the generals and strategist
(swap the commander for a different one). Then, swap those free
generals and the commander for the generals on the weaker army.
Another benefit of this is that later in the game, when you want
to expand, you can set up armies with only a commander (smaller
armies allow for more armies), and send them out toward cities
you want to take. If you think that you might have to fight a
battle to take a city (if it is not empty), use the general swap
trick for an instant army.