There are no easy way to win this map although there are some sure ways to loose. As you play along, you will realize that your mighty Barbarian is not so mighty anymore with a lot of units crossing the 50 barrier. Bunch of spiders in a citadel are 55, Gryphon becomes 60, Heavy Cavalry with Level 4 Horse Lord are 60 and Wolf Rider with a level 4 Ranger at Forest is 45 with 16% Ambush, Elements attacking with a level 4 Valkyrie are 54/3 and I am not even talking about level 5 heroes with Demons. As your high level leadership/chaos heroes are dwarfed by the Great Archon, your Assasin is not assasinating all that well with crusader+ranger or paladin warding.
So this game map requires a lot of maneuvering, holding key cities, vectoring, scouting, killing the enemy scouts, intelligent resource management, knowing where to attack when to attack etc. Besides the general rules of expanding in multiple directions and scouting early, holding the post cities, having hero presence at all the battle fronts, I really don't have a lot of suggestions, but I have a few remarks.
MAP:
The Map is divided in 4 classes of regions.
CLASS A: Northeast, Northwest, Southeast, Southwest these are the starting points and surrounding regions
CLASS B: At East and West there are elements cities. They are very important, easy to reach and easy to take down.
CLASS C: The power cities that are surrounding the center. They provide power unit production. They are harder to take down,
CLASS D: Cities and the ruins at the Central region.
Ignoring the center is one of the sure ways to loose this map. There are several moderately easy ways to take the center IF YOU ARE LEFT ALONE THERE. All you need to do is take down the defense on one ruin first. It will give you 4 elements and very good items that you can use to take down the other ruins and the cities. Or get the bless site first take the Shayatins Mask then proceed. However the problem is either you will loose a lot of troops to take it down or put your heroes to risk. If your enemy is near, and he should be, they can finish you off.
HEROES:
Every hero will work if used properly, no hero will work if not used properly. Know your heroes, know their strength and their weaknesses and don't expect too much from them.
UNITS:
There are plenty of two turn meat units that you will get when you occupy surrounding cities. Each of them are very useful. However there are two units that you have to train.
a) Devil: Although unicorn may work early in the game, there are plenty of moral and fear units. Elephant are the most popular choice, pegasi-medusa making occasional appearance but surely you will face the red dragon. Unless you receive lots of Devils as an ally, you have to produce them at some point.
b) Great Archon: Although Archon will be sufficient earlier, sooner or later you will be force to train one. as the heroes level up.
I think these are the two units that has no substitute. All the others has substitutes. Even elephants who are the most popular choice in this map has substitutes. You can go with Mammoth-Pegasi or gather some golds and use Green Dragon-Red Dragon combo for speed+moral. You need to produce most of the stack bonus units. At least one speed unit, one moral unit, one fear unit, one siege unit and possibly your ambush unit. You will also need city defenders and power hitters.
In a typical game I use all of the heroes and most of the stack bonus units.