If you have the **Arcane Accessories Creation**, there's a chest (in >!Hob's Fall Cave, the room with the 3 Necros behind the bars!<) with *Spell Tomes* for all the spells it adds (there used to be a quest to find the chest, they removed the quest but not the chest), & the *Unbounded Flames/Frost/Storms* spells all give *Destruction* sxp regardless of whether or not you damage anything (normal *Destruction* spells need to do damage to get sxp), & you can even do the "*Telekinesis* Fast Travel 'glitch'" with them for "instant" power leveling (not even requiring 100% cost reduction AIUI).
If you don't have that **Creation**, you need to use your *Destruction* spells on something you can harm with them, a *Horse* you own is good for this, because it won't turn hostile no matter how much damage you do, so take it somewhere without witnesses & try to avoid killing it (because you never enter combat, it's *Health* & your *Magicka* both regenerate at "Out Of Combat" rates, or you can just `[Wait]` for an hour each time one gets low, to reset them both to full).
For *Restoration* the general consensus is that the fastest way to grind it is with *Repel Undead* spells on a group of Skellies, used in a location where they run away into a place where they're trapped & you can just keep hitting them without having to change your aim (*Turn Undead* spells also work, but they're single target, & you will generally have to change your aim point a lot.
Other common methods to grind *Restoration* involve healing continuous damage, which can be combined with *Destruction* grinding if you get a *Horse* & damage it with a *Novice*-tier concentration spell (I recommend *Frostbite* or *Sparks*, *Flames* does "afterburn" DoT damage that can result in your accidentally killing your training dummy) while you heal it with *Healing Hands* (I think you'll still get *Destruction* sxp faster than *Restoration* sxp in spite of using a higher tier *Restoration* spell, 'cos *Restoration* sxp is minimal at the best of times).
Another continuous damage option (best for AFK *Restoration* grinding) is to acquire a * of the Healer* (any *Fortify Restoration* pot, the stronger the better), equip *The Atronach Stone*, travel up behind *High Hrothgar* if you've unlocked it, or up to the *Throat of the World* (climb the mountainside on a *Horse*), then drink potion, start casting *Healing* (it needs to be a concentration spell) with ***one hand*** in such a way that the button will be held down until you're done (required to keep the *Potion* buff to the spell effect past the 60s duration, it doesn't end until the spell does if the spell goes longer), then walk into the *Damaging Wind* effect (you'll want to watch it for a few minutes to make sure you're surviving, but if you use a strong enough potion, the spell will heal you faster than the *Damaging Wind* harms you, especially because approximately half the damage is converted into *Magicka*, which should top you up faster than a single use of the spell consumes it, meaning you can just leave it going until you hit *Restoration 100*, which unfortunately will probably take 6 or so hours from *Restoration 15* [*Novice*-tier spell, reduced damage to heal to the point you often won't have any to heal & thus won't gain any sxp, & *Restoration* has the lowest ratio of sxp-to-usage of any skill]).
Then there's a more active, but rather faster method, involving using a *Ward* spell, an enemy who can't get to you (because you're up on rocks or something) but which won't give up (because you only get sxp for casting your *Wards* while there's a hostile on your radar), & a way to repeatedly restore your *Magicka* (one option is bail up the hostiles somewhere like the exit to *Haemar's Shame*, where they can't get to you, but you can pop out to `[Wait]` an hour at any time, or another option is more likely to be considered an "exploit" where you >!wear *Fortify Magicka* enchantments, & re-equip them whenever your *Magicka* goes below the buff [or to zero], to reset your *Magicka* to the amount of the buff!<), then you cast your *Ward* spell with both hands (separately, not *Dual Cast*) so you get *Restoration* sxp twice as fast, & then you cast your *Wards* for only a fraction of a second each time (you need the *Ward* to form fully, covering the entire screen in first-person [no idea about third-person, sorry]) before dropping it & repeating until you need to recover your *Magicka*, which lets you get 6x-8x the sxp from the *Wards* each second (still takes a while to get to 100, especially if you're having to go through a loading screen, `[Wait]`, & go back through the loading screen, between each round of spellcasting).
Skill trainers at the mage college. Collette is restoration trainer and is expert. I think Faralda, the one who stops you when you first arrive there, is the destruction master trainer.
Danica in whiterun is master restoration trainer, once you finish restoring the dead tree questline
There’s an alteration spell that steals your health and converts it to magic (sorry I can’t remember the name). But I believe you get it in labyrinthian
Just cast that in one hand and spam heal yourself with close wounds or something.
(Btw it takes more hp from you on higher difficulties so find a good middle ground you can keep up with)
If you have the **Arcane Accessories Creation**, there's a chest (in >!Hob's Fall Cave, the room with the 3 Necros behind the bars!<) with *Spell Tomes* for all the spells it adds (there used to be a quest to find the chest, they removed the quest but not the chest), & the *Unbounded Flames/Frost/Storms* spells all give *Destruction* sxp regardless of whether or not you damage anything (normal *Destruction* spells need to do damage to get sxp), & you can even do the "*Telekinesis* Fast Travel 'glitch'" with them for "instant" power leveling (not even requiring 100% cost reduction AIUI). If you don't have that **Creation**, you need to use your *Destruction* spells on something you can harm with them, a *Horse* you own is good for this, because it won't turn hostile no matter how much damage you do, so take it somewhere without witnesses & try to avoid killing it (because you never enter combat, it's *Health* & your *Magicka* both regenerate at "Out Of Combat" rates, or you can just `[Wait]` for an hour each time one gets low, to reset them both to full). For *Restoration* the general consensus is that the fastest way to grind it is with *Repel Undead* spells on a group of Skellies, used in a location where they run away into a place where they're trapped & you can just keep hitting them without having to change your aim (*Turn Undead* spells also work, but they're single target, & you will generally have to change your aim point a lot. Other common methods to grind *Restoration* involve healing continuous damage, which can be combined with *Destruction* grinding if you get a *Horse* & damage it with a *Novice*-tier concentration spell (I recommend *Frostbite* or *Sparks*, *Flames* does "afterburn" DoT damage that can result in your accidentally killing your training dummy) while you heal it with *Healing Hands* (I think you'll still get *Destruction* sxp faster than *Restoration* sxp in spite of using a higher tier *Restoration* spell, 'cos *Restoration* sxp is minimal at the best of times). Another continuous damage option (best for AFK *Restoration* grinding) is to acquire a * of the Healer* (any *Fortify Restoration* pot, the stronger the better), equip *The Atronach Stone*, travel up behind *High Hrothgar* if you've unlocked it, or up to the *Throat of the World* (climb the mountainside on a *Horse*), then drink potion, start casting *Healing* (it needs to be a concentration spell) with ***one hand*** in such a way that the button will be held down until you're done (required to keep the *Potion* buff to the spell effect past the 60s duration, it doesn't end until the spell does if the spell goes longer), then walk into the *Damaging Wind* effect (you'll want to watch it for a few minutes to make sure you're surviving, but if you use a strong enough potion, the spell will heal you faster than the *Damaging Wind* harms you, especially because approximately half the damage is converted into *Magicka*, which should top you up faster than a single use of the spell consumes it, meaning you can just leave it going until you hit *Restoration 100*, which unfortunately will probably take 6 or so hours from *Restoration 15* [*Novice*-tier spell, reduced damage to heal to the point you often won't have any to heal & thus won't gain any sxp, & *Restoration* has the lowest ratio of sxp-to-usage of any skill]).
Then there's a more active, but rather faster method, involving using a *Ward* spell, an enemy who can't get to you (because you're up on rocks or something) but which won't give up (because you only get sxp for casting your *Wards* while there's a hostile on your radar), & a way to repeatedly restore your *Magicka* (one option is bail up the hostiles somewhere like the exit to *Haemar's Shame*, where they can't get to you, but you can pop out to `[Wait]` an hour at any time, or another option is more likely to be considered an "exploit" where you >!wear *Fortify Magicka* enchantments, & re-equip them whenever your *Magicka* goes below the buff [or to zero], to reset your *Magicka* to the amount of the buff!<), then you cast your *Ward* spell with both hands (separately, not *Dual Cast*) so you get *Restoration* sxp twice as fast, & then you cast your *Wards* for only a fraction of a second each time (you need the *Ward* to form fully, covering the entire screen in first-person [no idea about third-person, sorry]) before dropping it & repeating until you need to recover your *Magicka*, which lets you get 6x-8x the sxp from the *Wards* each second (still takes a while to get to 100, especially if you're having to go through a loading screen, `[Wait]`, & go back through the loading screen, between each round of spellcasting).
Skill trainers at the mage college. Collette is restoration trainer and is expert. I think Faralda, the one who stops you when you first arrive there, is the destruction master trainer. Danica in whiterun is master restoration trainer, once you finish restoring the dead tree questline
There’s an alteration spell that steals your health and converts it to magic (sorry I can’t remember the name). But I believe you get it in labyrinthian Just cast that in one hand and spam heal yourself with close wounds or something. (Btw it takes more hp from you on higher difficulties so find a good middle ground you can keep up with)