Champion points, mundus stones, nirnhorned, and passives. Not sure specifically what passives but if you look at the skill trees you can find them relatively quick.
IMHO penetration is a secondary concern especially when IC update goes through.
PC NA
VR1 - Jar'eed - Khajiit Dragon Knight - AD
VR1 - Broad Tail - Argonian Templar - EP
All-Star Crafter Guild
The Sharpened Trait can give you more Penetration. So can Nirnhorned, but I don't use it for that on weapons myself. There are Champion System skills that increase this but it appears the Spell Penetration one only goes up to 1.5% (so only spend two points there). Armor Penetration seems to work OK.
EDIT Forgot about the Mundus Stones. You can use the Divines Trait to increase that effect.
Edited by Nestor on August 4, 2015 7:42PM
Enjoy the game, life is what you really want to be worried about.
PakKat "Everything was going well, until I died"
Gary Gravestink "I am glad you died, I needed the help"
Already answered above, twice, use the Sharpened Trait or Nirn Trait on your weapons. Put Divines on your armor and use the Mundus stone that increases Penetration.
Edited by Nestor on August 4, 2015 7:54PM
Enjoy the game, life is what you really want to be worried about.
PakKat "Everything was going well, until I died"
Gary Gravestink "I am glad you died, I needed the help"