Upgrade your Sage’s Tower to level 8 or 9 and then start farming level 6 – 7 goblin camps.
Don’t go for the camps that have level 8, 9 or 10 because you will lose too many troops.
If your Sage’s Tower is level 8 or 9, you have like 80-90% chance to get a relic after an attack.
You lose around 1.000 troops per fight, be sure to have resources to rebuild.
Wait around 20-30 minutes before attacking the same goblin camp again. Give them time to rejuvenate.
Train your hero from these attacks. Your hero should get 20 experience points.