If you plan to play Gems of War a lot, then you'll get this naturally as you go, eventually.
Also if you feel the need to get this quicker, here are some things to enhance your XP gaining:
- Lion Armor for your hero; gives +75% XP
- or, if you have money falling out of your butt every step you take, then buy the Deathknight Armor for +100% XP gold and souls ($49.99US)
- blue guild statue/guardian gives XP bonus
- the pet named Lucky gives 1% to 5% XP bonus, depending on pet level
- your VIP level can enhance XP; I haven't bought anything in this game with real money, so my VIP level is 2; but to max your XP bonus from VIP, you need to be VIP 17 or higher
- some special events gives XP bonus
- Ring of Wonder gives +50% bonus gold, souls & XP; currently on the Monthly tab of the Offers page for $19.99US in a bundle with gems, gold, gem keys and glory; this lasts for 28 days after purchase
- winning your guild war battles as a team daily gives you 100% XP bonus for 24 hours (thanks
Har Miggido)