Just id all blue armor drops as you go along and you'll get runes. Be sure to check with a rune trader npc to see the value of the runes. If it's not worth more than a couple hundred gold, they aren't worth salvaging to sell once you have enough runes for yourself and/or your heroes.
Armor can take one insignia and one rune each. If you try to salvage a rune you run a chance of destroying the item you salvage it from. THIS INCLUDES YOUR CHARACTER ARMOR! So be careful. You can use a Perfect Salvage kit to take runes/insiginia off your own armor but they aren't cheap and you'll be upgrading your armor a couple times any way. If you apply another rune to a piece of armor with a rune on it already, it will just over write the old rune.
I usually get head piece armor with the attribute I use most and add a minor rune of the same attribute to that then minors for any other attributes in my build (like Expertise for Rangers). The rest I fill up with one vigor rune, or runes of attunement or runes of whatever the health ones are called.
For insignia I still like Survivor, but I think everyone's moved to armor runes.
I'm pretty sure most of the above comments about runes were referring to buying them, or that your armor will be upgraded so don't worry. But they do drop in the areas you are in, so you should use them when you get them.