I'm currently level 35, wearing all ebony armor, except for the boots. A few pieces have enchantments, like extra magika and improved 2-handed. My heavy armor is up around 45. The menu says my overall armor rating is 186, which I thought was pretty good, but I'm still getting taken out at times by a single arrow or ice spike.

I'm sure I'm overlooking something, smithing perhaps? I haven't done any yet, do I need to? How do I improve my odds against the dragur deathlords and dragon priests?

Thanks,

I wear the DB armour, and my rating is 467 if I remember correctly. The best way to improve your AR is thorugh skill perks.

Yours seems a little low to be level 35 or whatever. Have you used any perks in the Heavy Armour tree at all? I hardly ever wear heavy armour at all, but I have used a couple of perks in it, and mine is over 200 when I wear my set of Ebony.

Smithing FTW.

Armor skill and perks are what you need. My level 50 light armor wearer is at 555 armor rating. Smithing helps also, since my guy crafted his armor and upgraded it to legendary.

567 in theory is all that you will need.

I was around 3-4 hundred at my upper 20s. My advice:
1. use a shield and switch to 1 hand unless you have points invested in 2 handed.
2. enchant everything you can with fortify smithing (only use grand/black gems for greater effect) & make a new set. Use smithing potions as well
3. increase heavy armor skill. an easy but boring way is to walk riversides until you find a few mudcrabs and let them go to town on you. use healing for a little exp boost
4. increase your health. do so at your discretion. unless you use spells you should find a balance between health & stamina

side note. I have 100 smith, 100 enchant, 70 something in heavy and have a set of Dedric after doing the above at 1120+ armor rate

Also armor has nothing to do with magic damage. You'll need resist magic for that

I was able to get a heavy armor rating of up to around 1400. I believe they put a "cap" of 500-600 without actually telling us ingame. I believe an armor rating of 300 or 400 is half decent.

A "good" armour rating is one which you find your armour grants you decent protection, but the game can still kill you.

the cap is 567, anything above that is pointless.

186 Armor Rating is really low for Lvl 35, especially with Ebony Armor. My Nord Warrior had about 300 Armor Rating at Lvl 23 with a set of non smithed Steelplate Armor. Now he's Lvl 42 or 43, with 900+ Armor Rating in his smithed Dragonplate Set (700 or so Armor with Otar mask equipped for extra Resists, since it's no longer a matching set then), but he also does have fully perked 100 Heavy Armor. But like others have said, all you really need is around 600 Armor Rating to hit the 85% Physical Damage Reduction cap. Even smithed Light Armor can hit the Armor Cap, and heavily smithed low end armor can hit it too.
One of the huge advantages i find that Heavy Armor gives over Light Armor when perked, is the "Tower of Strength" perk. With it, my Nord Warrior can take a full "Fus Ro Dah" to the face from a Draugr Deathlord, and he barely even flinches. My Dunmer Nightblade in Glass Armor get's hit with the "Fus Ro Dah", and she goes flying.

Also the power Ancient Knowledge gained from the quest Unfathomable Depths grants a 25% bonus from wearing dwarven armor. Except its bugged and gives the bonus to all armor.

I have an armor rating of 470 with Legendary Dragonscale Armor + light armor perks, and I hardly take any damage.

You don't say what difficulty level you're playing on. That makes a lot of difference. I play on Adept. My level 40 warrior (light armor, 2-handed) has an AR of 252. I don't even bother putting on a helmet 99% of the time (when I do my AR goes up to 380, but I don't bother unless I'm facing an Elder Dragons). I'm in no hurry to raise my AR. I don't need it on Adept. If I were playing on a higher difficulty setting, I might.

My Nightingale Armor gives me about 400 with 83 Light Armor and some perks to that. Also, Nightingale is upgraded to Legendary. My friend has a Heavy Armor and has like 800.

Why, over 9000 of course. But apparently 567 is the cap, so that will have to do. Shouldn't be hard with a little smithing.

I'm playing on Expert right now. I'm going to try some of the stuff people suggested here.

Thanks to everyone for their input.