- Raise enchanting to desired amount and then enchant your gear to reduce magicka cost. I would cap at 95% - 97% reduction, since above that makes the game too boring.
- Raise alchemy to desired amount and then make potions of fortify destruction and poisons of weakness to fire/frost/shock. For role-players, the best way to add the poison is to conjure the bound bow and add poison to it, and fire one shot before putting it away. That way, you are still using magic to do what you want.
You can get decently high destruction damage. Without glitches (but doing everything the game designers allowed), destruction does very decent damage. Calculations are pretty simple.
60 (Incinerate) * 2.2 (dual-cast) * 1.5 (augmented flames perk 2/2) * 2.77 (best fortify destruction potion I believe) = 548.68 That would be the highest damage you can get per 1 shot.
Note: I didn't include the DoT from incinerate because I didn't know what it is, but it is negligible.
For an even higher value, put a weakness to fire poison on the enemy, which makes the total 548.68 * 2.06 (best weakness to fire poison I believe) = 1130.2808.
And that is the highest you can get, I believe. Through legit methods. I understand why everyone is complaining about destruction (nobody wants to keep chugging potions), but, meh, it's not a huge deal. And I don't find chugging potions takes significantly away from roleplaying a mage. I mean, potions themselves seem pretty magical (they were in Harry Potter now weren’t they? lol).
Destruction is nothing compared to melee or archery (to say nothing of those two each combined with sneak perks), as these run up into the multiple k's per swing/shot, but it'll do when dealing with what the game throws at you. Easily.
I got potion values from here: youtube, /watch?v=HPjylMugGbA
EDIT: Corrected small mistakes.
