Best heroes
Shakti - starts with 3 stacks of troglodytes, has a high chance of getting Earth Magic, gets good secondary skills in general.
Gunnar - logistics specialist, high chance of Earth Magic, good secondary skills.
Alamar/Jeditte - resurrection specialists, Alamar also has scholar so he can teach res to someone else if he doesn’t get Earth Magic.
Build order
Turn 1 is almost always the troglodyte upgrade. Or in some cases, battle scholar academy, if there are no fights that you need to do on day 1.
After that, if the map gives you external dwellings for dragons, manticores, or minotaurs, you will usually build the portal of summoning.
After that, if you summoned minotaurs or manticores, you will usually go for the build path to build them in your town.
You will also build the Mage Guild and Mana Vortex as needed.
Best spells
Slow is usually essential, as most break will be done with army and mass slow. Shield/Stoneskin and Resurrect are very helpful in situations where the break cannot be slowed. Spells like Haste, Bless, Implosion, Dimension Door etc. are always useful and will be available in the best overall spells guide.