The only easy to level magic skill I've found is Illusion, via using the Muffle spell over and over...

In Oblivion I used to summon creatures and kill them with my destruction magic to simultaneously level both of the skills up. Unfortunately this doesn't work so well... while you can level up your destruction skill from harming your own summons, you don't level up in conjuration unless the creatures you conjure actually do damage, any suggestions?

I want to know this too. When I tried a mage and tried to powerlevel stuff like alteration it seemed you need to be in combat to get any skill exp. Conjuration help ofc but the mechanic is very different compared to Oblivion.

trainers

Or, you know, just use them in combat and forget about silly "power leveling". I've found conjuration to be absurdly easy to level, as you cast once then keep gaining skill ups as your minions fight (and you get skill ups in other things - armor, weapons, destro magic, whatever).

The basic system actually works very well.

Or, learn the various fortify enchantments, and use those to simply boost your skill directly.

Exactly, In Oblivion if you wanted to level efficently you had to be fairly exact in how you leveled your skills if you wanted the best attribtue bonues. Raising a major skill by 10 and two minor skills by 10. In skyrim that aggravation is all gone. You don't need to grind to level efficently anymore..

Get the atronach stone
Go to high hrothgar
Go to the magic barrier that damages you
Walk into it.

*The atronach stone means you absorb some of the magic that hits you so while you are in the barrier you have very quick magic regeneration, essentially infinite magicka if you'r casting a weak spell.

Continually cast a heal spell for restoration.
Or you can cast a heal spell in one hand and another spell in the other, e.g: muffle