Feel free to post your favorite tactics what you like to use with different races :)

HUMAN

When my hero is established I like to rush out with as many knight lords as the army set up points allow me to buy and convert as many mines as possible while a builder prepares my base. I will often try to hunt down the enemy or at least one or two before returning to my base.
If there are multiple enemy's I destroy one before returning to my base where I have been producing lots of pikemen. I then send the pikemen in to destroy buildings but mainly keep a hero occupied ( also a great way to waste a hero's mana) while my hero and knights do most of the work.

I love my Dark Elf Summoner, seriously can't get over how good this race/class combo is.

So I've been grinding for exp on random maps: Medium map, low resources, 12 army points. I went up against knight+lord, then stepped it up to 1 prince, and now I'm doing 1 warlord

For 12 points i take 2 Sorcerors and 2 Dark Archers - Sorcerors are the dark elf's ultimate unit, only tier 3, yet are so useful for sniping units, wiping tough armies with Pillar of Fire, and spawning zombies for free builders on the fly. The dark archers are there to add a little bit of ranged DPS, but mostly to die instead of the Sorcerors (sorcs not dying is critical to my strategy)

At the start I'll summon quasits once (at my casting skill i get 2 for 1 summon) and send them out scouting one way, while my ranged mob scouts the other way, looking for mines and the enemy hero, while my hero sets up the initial capture.

I'm looking to snipe the enemy army early with my ranged mob. The AI will usually blunder right into my pillars of fire from my Sorcerors, the primary threat would be a wizard hero dumping some AoE spell on my troops and wiping them easily, so I try to avoid heroes until their retinue is dead. So, snipe and run, nuke the cavalry, easy pickings.

Then begins the pressure phase. I'll group up my hero with the ranged mob and go after the enemy hero or his base. Spot the enemy hero, I drop a summoning circle and unleash my secret weapon - 3 to 6 Elite Succubi out of thin air. This easily kills heros or sends them running back home. I'll summon zombies with my Sorcerors, or if they just spent their mana on pillar of fire I may save some mana on my hero to summon quasits, then we start building crypts and trees around the enemy's base, spam out skeletons and other dark elf units situationally. Its then a matter of waiting until sorcerors are teched at tier 3 when I can easily mass enough troops to topple their base.

EZ exp