Skyrim – walkthrough and progression.

I maxed out Sorcery to 100. By the way, you get the most experience if you summon two swords at once. You can do it without Atronachs – just run around the enemy, summoning swords as your mana regenerates. This is how I leveled up Sorcery from 90 to 95 before the boss in Saartal.

Enchantment also started to level up much slower. According to my calculations, to level up Enchantment from level 90 to 100, you need to enchant 60 items (!). And that takes a very long time – you need to craft them first, and then search for crystals for sale in all the cities.

Destruction, on the other hand, can be leveled up easily in battles, as well as Weapon skills. It's currently at 75, and only 10 of those levels were gained in battles with Atronachs (+ 20 base levels).

I found "Equilibrium" (while searching for the Staff of Magnus). Unfortunately, even with it, Restoration levels up very slowly. But I found one way: buy "Greater Healing" at the College, but definitely don't learn "Expert Restoration Magic." Take "Equilibrium" in one hand and "Greater Healing" in the other. Spend mana, activate "Equilibrium." Then, when your health is almost zero, use "Greater Healing." This way, you'll gain the maximum amount of experience (apparently, it depends on the amount of mana spent and the amount of HP healed).