Is there no easy-ish way to level destruction? I tried the whole stand on a rock/ledge and cast at Giants, but they die and I've only gotten like one level tops... I can clear out whole camps with spells of any level and not get any significant progress. The only remotely decent progress I've found how to get is to use Sanguine's Rose to summon the Dremora and use Incinerate on him 'til he dies. For some reason he never goes hostile with this spell so no having to run away from him, and he has way more HP than a Frost Atronach (highest level Atronach I can summon currently).

For all the other schools there's a way to practice. But even though you see your fellow students practicing their Destruction magic at the University, there's no way to practice without combat. In combat I either kill them in one hit, or get clobbered.. either way ends up giving painfully low chances of skill experience. What I wouldn't give for a magical training dummy.

Hey ah, this is just a thought, but maybe if you just use it when you fight stuff it will increase.

You don't need to have 100 in a tree before you use it for what it is used for dude.

Yeah, see there's a problem there. I'm getting up in levels but started out fighting with melee weapons. So I don't have access to spells strong enough for basically any enemy I encounter except a skeever. If I go to a tomb where things can withstand more than one hit, they destroy me in short order. So I'm sitting at an either-or scenario, either I have to kill thousands of random wildlife creatures lower level than bears, or get killed trying to level destruction.

Invest in dual casting and the impact perk, and enchant some gear to drop your destruction cost as low as you can. At that point, it's just a matter of timing your shots so foes can't advance on you, and making sure you are taking enemies on one at a time. Leveling destruction is still gonna be kinda slow though, but at least this way you can use it as your main killing skill.

Cast the biggest spells you can, runes give much more xp than earlier spells.

Basically from what I experience is change to master and go on a critter low level mob toasting runs. I have gear that gives me free spells so its basically spam spam spam. You can use the cheat method of casting on a companion or placing a basket on the head of a unkillable NPC and skill up that way.

do the training with vilkas from the companions (first quest) and when you are in outside with him simply SPAMCAST your strongest spell on him. reached destruction 100 in less than 2 hours this way. he will state that you should fight with weapons when you cast at him. no spell really damages him since its a training encounter he does never loes hitpoints. still takes a while and can be kinda annoying but with zero destrution cost gear its duable under 2 hours by using thunderbolt. this is what i did.

replay the areas you went to at lower levels.
Going back through that tomb outside riverwood for example.

When you first clear a place you 'lock in' the level of stuff in there, so it will be easy if you go there again.
I did this in reverse, trying to get some 1h skill up when destruction was my main combat skill.

Also, making sure to drop 5 trainings on it at every level up is handy too.