For the most part, there's spells you won't be able to touch, so there's always that. Unless you're up against a nation that can use them, don't bother worrying about it too much. So here's a trick worth poking into. Open up a spell research tab and hit A. That should narrow things down considerably to just the air spells you have. Now, the list is still considerable, but in this list you will find your bread and butter spells, from summoning to rituals to spells that harm your foes (and some that harm everyone). If you wanna know what the other filters are hit ? and you'll have a nice handy list to narrow things down further.
If you're playing a nation, chances are there's a guide for it so those tend to list what kinda access your mages would have, as well as troop composition and the like. For death nations you want to raise the dead in battle to create instant chaff, air nations tend to lightning spam, and that sorta thing, so you'll eventually limit it to what you'll get the most use out of pretty soon.
Most importantly, if I have one complaint with dominions at the moment it's that summoning units and crafting items don't fill you in on what you get. Crafting 6 is important, but you wanna know how important it is, and it's hard to do that without knowing wat you could craft at what level. And for conjurations all you have is the game decryption you get, which doesn't always tell you everything you wanna know. Trick to that is using the
dom4 mod inspector, which looks at all the vanilla units and links things, so you can look up a spell or an item and get the exact stats and crafting requirements.