[Aleph]

If you aren't using magic, you're not advancing up the only tech tree there is in the game.

The classic uses of non-national low level summons are Vine Ogres and Corpse Men (technically, a construction not a conjuration). Both benefit from decently tough basic frames but can be summoned cheaply in large numbers with the right equipment (see manual). You probably won't be able to put together overwhelming numbers of them until mid-late anyway (since you'll want maybe 5-10 properly equipped mages casting the appropriate spell monthly, and earlier in the game research is king), but they are available quite early if your basic forces need a bit of backup.

One battlefield spell in particular you might want to look more closely at is Raise Skeletons (Enchantment 3). It is one of the earlier spells in the game that you can use to obliterate indeps without much effort, especially in conjunction with solid ranged troops. It's a nice spell because a. it doesn't miss b. it doesn't have a range at which the computer won't cast it c. it gives you endlessly reusable chaff to eat up whatever casualties indeps might otherwise inflict which would slow down your momentum. Particularly nice against heavy cav, to have them break their lances against.