In general, you can either choose to try to reduce their effective armor, or ignore it.
There are plenty of ways to reduce armor, such as the Spitting Raptor, Rust, Acid Ball, and through various spells that provide Piercing. If you don't have a few of these in your book, then you can try to just ignore the armor.
If you are going to ignore armor, then you might go about it in one or two ways... either get a lot of dice in attacks and look for critical damage to get through the armor, and/or you can use attacks that deal any of a host of conditions that put the opponent at a disadvantage in a different way. Getting a Daze or Stun, for example, while doing several dice of damage is good in hurting the enemy and helping to protect your own position. Also, direct damage spells will bypass armor... so a nice Ghoul Rot, etc. curse strategy, or a multiple-Burn concept can help if you are going to ignore armor.
There are some specialty spells that can work to help or hinder these types of strategies.
For example, if the enemy Mage is stacking armor, try to make sure that he can't keep a Veteran's Belt equipped, as you will then need even larger numbers of dice in each attack on him to do any real amount of damage.
The Elemental Cloak or Storm Drake Hide, for example, can reduce the chance to be impacted by Lightning Bolt and other attacks that impose conditions.
Geyser is particularly useful in removing burns.
There are plenty of ways to keep Corrode conditions off, from simple swapping of torso armor to Rain Clouds used as anti-acid pills, that will need to be considered also.
My own way of looking at it... in general, I don't usually care if something has only one point of armor... it's at the 2-3 level where I start to look to reduce armor through Corrodes / piercing attacks. I usually don't bother at the 4+ armor levels, and simply treat the target as being effectively Resilient. It just takes too many actions and too much mana to play the counter-armor game at that point, in my opinion.
I hope this helps some.
