A.I. Tactics
You should take advantage of the artificial intelligence of enemy units, which as the Game Banshee website notes, isn't overly advanced, whenever possible. Enemy units will give up pursuing your damaged soldiers quickly, so make use of hit-and-run tactics: if your unit is damaged, move it back out of your enemy's reach and send in healthy units. Enemy units will focus on the newcomer, and you can be free to send your damaged unit back in to attack again.
Assembling Resources
You'll need to accumulate two types of resources to expand your empire in "Dragonshard." The first are the dragon shards themselves, crystal-like objects that regenerate once you've collected them all by falling from the sky. You'll also need gold, which doesn't appear in such a way. Instead, you'll have to head into the game's underground areas and explore the buildings within, or else collect it through taxes.
Undergrounds
Underground areas are useful in that they give you experience, items and gold, but they're dangerous. Note that you can only send certain units --- champions and commanders -- to the underground, but one way of increasing the health totals of the units you're sending is to accompany the commander or champion with soldiers. These add their life points to their leaders as they enter the underground. Also consider adding a rogue character to your group beforehand. Rogues are important underground as they can deal with traps and open treasure chests.
Units
A few of the game's units have certain rules you should consider. Rogues can use a cloaking ability to stay hidden from enemies, but in this mode they won't react as usual to commands. For example, an attack-move command won't allow them to attack; you'll need to directly utilize the attack order. Also note that champion and juggernaut units don't contribute towards your overall population, a limit that otherwise restricts the number of units you can control.
The Nexus
The nexus is the central hub of the empire you command, and it begins the game with four blocks of building pads, where structures can be raised as the game progresses. If you want to train up your units to higher levels and thus make them powerful, consider creating multiple training buildings of one type on the same building pad. Training buildings also allow the building of monuments, structures that strengthen your units, as well as raise your population limit.