I've started a new Skyrim run a few days ago, and since I was looking for a harder challenge, I've set the difficulty to the highest setting, legendary. I'm leveling conjuration, two-handed and heavy armor - at least that's what I'm trying to. The problem with the latter is that most enemies can one-hit kill me (I thought this would stop after a few levels, but I'm at level 18 now, still no change), so I have to hide behind my follower (Lydia FTW) and summoned creature. That works fine for killing enemies, but since I'm barely hit at all, my armor skill doesn't level up. What can I do about this? Is there a good way to level my armor skill? (please no suggestions that involve lowering the difficulty) The only things that don't kill me in one to two hits are like mudcrabs, and even those come dangerously close ...
As a level 14 character with 200 displayed armor rating and 200 health, a mudcrab hit on ledgendary does ~15% of my health (I guess 20-30 hp).
Your problem is probably that your armor rating is too low. Wear armor (not clothes) on all four body slots (head, chest, hands, legs) to get the extra 100 hidden armor bonus. Upgrade all your armor at the blacksmith to increase your armor and spend perk points on your armor skills.
The basics of leveling armor skill are: get hit, don't block and don't die. If you block, you get block skill instead of armor skill. If mudcrabs are the only foe you can survive, level your armor skill with them.
However, leveling armor skill doesn't really protect you... The best way to increase your armor is to get some armor perks. If you aren't going to get the perks, then leveling the skill can be ignored.