At the beginning of the campaign form your main line with a half dozen zombies. They're cheap as dirt, and the only thing they accomplish is tying down the enemy's line. Don't expect them to do anything except take a ton of damage. You won't care if half of them die every single battle, because raise dead is amazing.

Send your fliers up the enemy's backside after the front lines have engaged. Your beginning bats are incredibly weak, but they're fast, and if the enemy is already attacking the zombies your bats can do decent damage, and flanking always does great morale damage. (Also send any other hard hitters, like vargulfs into flanks, unless they need to take out archers.)

As others mentioned, doggies are great for hunting down archers.

So, to reiterate, zombie front line (maybe 5 or 6), hard hitters and fliers flank, fast movers kill archers, profit. Don't have any of your hard hitters taking on an enemy that isn't being swamped by a zombie unit.

You can win battles that autoresolve is convinced you'll lose horribly by doing this.