Gear (hats, robes, boots). Go to the Bazaar and shops and get the gear that has resistance. Or if you have them, go to the Crown Shop and buy gear there.
gear & pet, essentially anything you can equip can bring better resistance depending on whether that item has it in its stats, there is no base resist or damage, it's all based on equipped items, gear, pets, etc.
If you are Ice, you can get global resistance on your gear from early on. Other schools can't, unless they buy gear from the crown shop or hoard packs.
Once you get to level 55, you can craft gear that has resistance!
Level 60, you can farm WaterWorks which has gear with global resistance for every school.
Pets can give Spell proof and spell defy, both give global resistance.
These are the main ways to increase resistance in the game, pending on what level you are.
any gear will work for resist (lot of player) goes for jade gear because they have high resist gear in keeper lore pack but get a spell in that pack to like (keeper of the flame/Myth) (brimstone revenant/Fire) (luminous weaver/Life)
AND maybe try Shaman's lore pack (new Azteca Crafting Spell) because don't think we know anything about lower level wizard for that pack (ice gear in there) lucky getting ice robes (High Resist) level 80 that i saw (IAmChazz) youtube channel (got one ice resist robe for level 80 at 16% resist but more pack later (begging for winter moon spell)
but more pack later (begging for winter moon spell)