So, to help out, I've made this guide on how to make the game harder by limiting yourself on the things you do, instead of going overboard and become God-Like...
~Weaponry~
-Damage-
Any weapon is fine to use but if you truly wish to keep challenges then best to make sure your weapons deal a damage of 100 or below. You can go a little higher than that if you wish to do so (I use a Daedric Claymore with a damage of 107). Limiting this is by far one of the main things you should do, the 2nd will be spells. Note: Your total damage shouldn't go over 150. I'll explain this more as I go on.
-Enchantments-
When enchanting your weapon, most enchantments are fine to use as long they don't do damage. When they do damage then make sure to add your weapon's enchantment damage with your weapon's main damage. My Claymore has two enchantments, one is absorb fatigue and absorb health. The Absorb Health will count as an enchantment damage and it does 25 points. I add this with 107 to get 132 total damage, which isn't above 150 so it is good by my standards. Absorb Fatigue doesn't count and wont truly matter.
-Potions-
I don't use potions but if you do, make sure they are about %25 - %30 increase max. Maybe lower, if you have enchantments. I'ma use a %25 potion as an example. Times %25 by your weapon's damage, which mine is 107, and then add your total damage. {(0.25 * X) + Y // X being your Damage and Y being your total.} For me, I have to do this: ( 0.25 * 107 ) + 132 ) 0.25 times 107 = 27 (If rounded) then I add 27 to 132 and get a total damage of 159 which is over my 150 limit. Therefore, I need to use weaker potions. Note: When doing this, always round upward. Also, add any damage your poisons do as well but this mainly doesn't matter.
-Perks-
Any Perk in the 2H, 1H, and Archery Skills are good to use, except those that increases your damage when you do a certain power attack. 2H and 1H has a %25 damage increase when doing a standing power attack so using this may not be the best. If you have to get this perk then don't use the power attack TOO much. 1H's duel wielding perks also has a damage increase. I say don't use them at all!
-Duel Wielding-
Duel Wielding is different then using one weapon. One weapon will always be around 100 damage. Duel Wielding weapons should be around 50, since you will add the two together to get a total of 100. I believe all 1H weapons are below 50. Some shouldn't need to be upgraded, so remember this.
~Armor~
-Main Armor Defense-
Your total Armor rating shouldn't go above 500, or at least not by much.
-Enchantments-
Don't use enchantments that fortify your weapon skills or armor skills. All other enchantments are fine to use as long you don't have over %50 in some. (Don't go over %50 Resist Magic, Fortify Magic, etc) Count your enchantments from Rings and Necklaces as well!
-Potions-
It is best not to use potions that boost your armor rating in some way unless your armor rating is very low already...
-Perks-
Use the main 5 perks but using some of the other perks can easily make high level armor go over 500 is be very careful on your perks when using high level armor.
~Magic~
-Destruction-
#1 thing you should know. Don't make it so you can cast all spells without using magicka! This goes for all schools! As for Destruction, don't constantly cast high level spells. Mix it up a little and use lower level spells as well. Be careful what perks you use as well, since some perks can increase damage. Only perk I recommon not using is the one that allows storm damage to turn enemies to dust because this will allow your to get an auto-kill if the enemy is low enough on health, which is annoying even when you can't do that much damage!
-Restoration-
Nothing to say here except don't over use spells that harms undead and makes them flee. Also, if you are using a ward, consider its armor rating. Don't want to go over the limit you've set yourself, or my own if you are using my limits. Restoration perks seems fine to use.
-Alteration-
Don't spam paralyze. Paralyze is the #1 spell in Alteration that can easily make the game easy, specially during 1v1 fights. Don't use the spell that allows you to ignore 80% damage. That spell is completely over powering, if you ask me. Also, remember to add armor spells to your current armor rating. All other spells will be just fine and Alteration perks are fine though I never use them.
-Illusion-
Nothing to say here except only use majority of high level illusion spells for fun and not for combat. All perks here are fine to use as well.
-Conjuration-
This is prolly the most over powering school. I personally think it doesn't matter what spells and perks you use as long you don't use any of the Thralls. Dead Thrall specially since you can get two mages that can destroy anything for you, basicly. You can, if you wish, not use Twin Souls since it can be over powering as well.
~Other Skills and Perks~
You can level all Skills as you wish without becoming God-Like. Don't worry about that. Just remember to be careful with perks. Any Perk that increases Damage and Armor Rating you should use wisely. (Like that one perk that allow you to do 15 times more damage with daggers when sneak attacking.)
That is all for now. Contribute your own thoughts and ideas, if you wish.