When starting off, pick a higher HP unit like halbs.

Avoid units with rstr in the beginning.

Dont promote units past the following:
Dont promote past app until 3rd LT
Dont promote past adv until Major
Dont promote past vet till Major general

If you want a ranking army start picking up healers between 3rd LT and Lt col and make sure to add minimum of 15 maximum of 24 by Field Marshall.

The best armies either use high hp (example rifleman) or low hp (fighters) and not a combination of the 2. A half fighter and half rifleman army sucks.

Dont be afraid to lose the freeby at the next promotion if it doesnt work well with your army.

the secret is to managae your income by holding off promotions and maximizing the total number of units you have. The more units the better. Nothing worse then an army at the hard cap with low unit count.