The types of spells that work are things like luck spells, positivity spells, confidence spells, etc. Subtle things. It's not the spell itself that makes it work; it's the caster's belief, knowledge, and practice.
That being said, of course there are spells that don't work, such as flying spells, reanimating corpses spells, and shape shifting spells.
If you want some examples of the types of spells that work, check out spiritual spells. Most of the types of spells put in that category can work.