If you do not have a tag that identifies you as a spellcaster, you cannot cast spells. Easy.
If you do not have a tag that specifies an effect, you always take a consequence of magical fatigue equal to the power of the effect. This status cannot be lessened by a reaction. This is in addition to any consequence resulting from a 9 or less on the roll.
Pathfinder and D&D have way too many spells to take a tag for every spell a full caster has under their belt. When in doubt, consult with the Narrator (aka GM). I will list a few examples.
A tag [Fey-Blooded Sorcerer] might take [Fairy Charm] which would serve as Charm Person, Charm Monster - any number of spells that work on the principle of “Let’s be friends.” Of course, a more powerful target will require more power.
A [Wizard] with a [Fiery Destruction] tag can cast a simple flame bolt or - with enough power to add an area of effect - a Fireball.
A [Priest of Pelor] with [Healing Magic] could cast a cure wounds, but also disease, poison, etc.
So, let’s say the Priest wants to cure someone who has run afoul of a Wraith and suffered Constitution drain (which would be some sort of status - let’s say [Life Force Drained 3]). In pathfinder, this requires a Restoration spell, which the Priest does not have a specific tag for. He can pray for it, though. This would be a prep action he would do while camping, using Priest of Pelor and Healing Magic, plus or minus any other tags and statuses that are relevant, which he could use to create a tag [Restore Life Force] and now he can cure it.
Each casting class in D&D/PF has a slightly different set of parameters. I’m trying to walk the line where I keep that flavor, but without getting crazy granular. So, this is what I’ve come up with. Each spellcasting type will have a narrative limit.
Wizards will need a [spellbook] tag (though a fully committed Wizard will probably want it to be a theme) and can prepare various spells using the same kind of prep action as the priest in the example above. Alchemists will need a [Formula Book].
Sorcerers cannot improvise effects - if they don’t have a tag for it, they can’t do it.
Clerics, Paladins, Inquisitors, etc. need their Deity’s Favor - anyone who plays a cleric will need to agree with the Narrator what the tenets of the Deity’s faith are. If they violate those tenets, no magic until they have redeemed themselves in their deity's eye.
Druids and Rangers need to be in Harmony with Nature - they can take a status of Civilized which will impede their spellcasting, or they could lose their power altogether if they really go against Nature.
Bards have to perform. I know it’s not necessarily D&D canon, but there is no subtle Bardic Magic in my world.
Components, ceremonies, etc: The last thing I think anyone wants to see is a 2e style Quest for Bat Guano so the wizard can cast fireballs. But, I do love the power of exotic materials, holy symbols, dramatic incantations and so on. Anyone who wants to “power up” their spellcasting with components such as these can do so. But you need to have the tags and it has to be relevant. A priest with a [Holy Symbol] can use it to empower his spell casting. A wizard with [butter] can use it to empower his [Grease] spell. And any caster can take a prep action to create the proper [Incantations] and [Mystic Gestures] to juice up their spells. But nobody HAS to. You can just use your action to cast your spell.