So you finally got the hero of your dreams this can mean only 1 of 2 things. Depending on how far you are into the game you're either going to use the hero sacrifice feature or take the long haul by grinding out exp. My tips in gaining maximum hero exp are as follows
Hero levelling from 1-40 solo small boss such as Unforgiving Mage, Earthsplitter Vam, Enchantress Rosha. (Note) taking a lvl 1 hero to a higher lvl boss will not give more exp at this stage so rule out DreamWeaver,StormLord and Undead Monarch for now. Same applies to dungeons.
1. Hero reaches lvl 10 and learn skill Acclaim I (+20 units)
2. Hero reaches lvl 30 and learn skill Acclaim II (+40 units)
3. Hero reaches lvl 40 equip with a Frenetic suit (+50 units)
4. Add 8 sunbeam crystals to your frenetic suit (+80 units)
OK so your hero has reached lv 40 and you have completed steps 1-4 so your hero now has + 170 units to add to your units from research (lvl 100 = +300 units) giving a total of +470 units not bad for a lvl 40 hero.
Hero levelling from 40-60 again moving to a high end boss will not result in more exp so try Phantom Dez,Krail,Stygian
5. Hero reaches lv 60 remove Frenetic suit and replace with Harmony suit (+85 units)
6. Add 8 Golden Keystones to your Harmony suit (+144 units)
With +40 units from Acclaim II your Harmony suit now gives you a cool +269 units again with max techs that's +569 units at lvl 60
Of course the whole point of this is to gain as much exp as possible as fast as possible and it goes without saying more units = more exp that's why balanced heroes lvl so quick !!
7. Depending on your strength you should now be able to add your lv 60 hero to your team for dungeon 60,70,80,90 hell mobs and sub-bosses
8. Level 80 has arrived so now you either dump the harmony suit and lose the unit bonus or you can keep grinding away with it. It's possibly cheaper to keep going with the harmony set for unit bonus as you would need Arctic lights at this point to make up for the decrease in units thus saving you gold as you will by-pass orange equips from lv 73-80 and start buying equips when you reach lv 90+.
Using this method you can have your hero at lvl 60 in just 1 day and lvl 80-85 after 3 days.
Other useful tips:
Use the coliseum by assigning just the 1 hero for full exp per 60secs (Better effect when VIP) 10hrs offline training adds up.
Ask a friend or alliance member if you can tag along on some boss runs for easy exp.
You can also solo a boss yourself (strenght depending ) with just 2 heroes , your best tank and your new hero. Doing so you will gain more exp or about the same as leeching with a friend. Assign archers to your tank and T2 mage to your new hero and assign them both in the dodge position of Right Feint.
I do this from time to time at Enchantress Rosha and my hero gains 112k exp per run . If you run Rosha with 6 heroes your new hero will only gain 33-37k exp so try with just 2. It usually takes 3-4mins max per run with just 2 heroes for over 110k exp compare with Undead Monarch it takes around the same time with 6 heroes gaining 100-125k exp each but your new hero won't gain that kind of exp in a team of 6 heroes on a high lvl boss.
Hope this helps in the future and happy hero levelling!