This is what I use to clear the stages

Relic Ruins - Earth/Spirit
Thieves Cove - Earth/Air
Skeleton's Tomb - Fire/Spirit
Flaming Wildwood - Fire/Water, Earth/Water
Cold Rock Crags - Earth/Air, Spirit/Earth
Faerie Forest - Fire/Spirit, Fire/Water
Writhing Cascade - Air, Earth/Air
Guardian's Crossing - Earth/Spirit, Earth/Air

The second 8 stages are a little more difficult, because the main boss is usually strong against what I use to clear the stages leading up to it

Sparkling Steppes - Fire/Spirt (Main boss is Water)
Blazing Tides - Earth/Water (Main boss is Fire/Spirit)
Cabalero Desert - Earth/Water
Sunken Carrack - Spirit/Earth (not really any one good combination)
Misty Marsh - Spirit/Earth (Main boss is Spirit/Earth)
Zephyr Plateau - Earth/Spirit
Haunted Citadel - Fire/Spirit, Fire/Water, Fire
Kingdom of Darkness - Stage elements are, in order, Spirit/Earth - Spirit/Air - Spirit/Fire - Fire/Water - Spirit/Fire- Earth/Air - Fire - Spirit/Air - Spirit/Fire - Spirit/Air.
I use Spirit/Fire, Spirit/Earth, Fire/Water (Main). Friends I use are Fire/Water, Fire/Spirit, Fire/Air, Fire (Depending on what's available)

For strategy, I fight through KoD down when friends are not being used for EB (and use gems to revive until friends are exhausted for the day) and start from Relic ruins and work up once energy is refilled until friends are available again. Cleared the first two revamped HM with a week left doing this.

Hope this helps and would like to hear any suggestions/improvements on element combos.