Type these codes in the game:
iamsuperman - Gain access to Farseer and Avatar
iamanexarch - Gain access to all exarches
iamawarlockman - Gain access to all warlocks
Keep Your Troops
Keep those troops alive. You'll never survive the later missions if you haven't nurtured your people and grown them into Exarchs.
Only Fools Rush In
Knowledge is power. Only fools rush in, so use your Mimes to scout the opposition. This will keep your army from stumbling into nasty ambushes.
The Right Tool
Use the right tool for the job. Pay attention to each unit's special abilities. Units with armor-piercing weapons should be used against enemy armor, while those with Scatter Lasers work best against the bad guy's infantry.