Reserves: came as a suprise to me, but you can have hundreds in your reserves. Just hire 295 griffins, put them in reverse, hire another 295, put them in reserve, repeat till you've got loads spare. My mage had 900 archers in reserve, for the occasions I needed sacrifice fodder.
Other than reserve:
I'm playing a mage, but my strategy is to use disposable summoned units to distract the enemy, and use ranged troops to kill them.
I rarely lose units.
Dunno how much mana you've got to play with, but in round 1 of every combat I summon a phoenix, it's very high initiative and speed allow it to reach the enemy before they move. I try and block a ranged attacker. As a warrior you might not have enough mana for that (40 mana for ancient phoenix), but druids summoning bears might be able to manage something similar. Maybe ghosts or vamps, since they can restore their numbers.
Most of the enemies attack the phoenix while the rest of my troops use ranged attacks against the enemies ranged attacks.
I use an Evil Beholders to control an enemy range unit, mainly to stop it attacking my troops.
By the end of the first or second turn all the enemies ranged troops are usually dead, I'll use my inquisitors to ressurect my most damaged unit, and use the Gift spell to allow the inquisitors to ressurect again. Giants jumping and area of effect enemies still cause me a few losses though.
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Harley-Davidson Hummer