For the early stage of development:
Against small units:
Wait for them to come to you... the summon should activate in time... Then send Fire Demons forward, with dogs supporting...
Against large units:
Push the Cerberi into the very corner and cover them with Fire Demons... Often the Cerberi manage to strike and run back...
Against shooters:
Well, here two things rule... Summoning reinforcements and Surprise Attack (which becomes available quickly even at early levels)
And by mid-game, you'll have horses (Soldier's Luck won't hurt) and Pit Lords and Succubi, of course... there are plenty of tactics then...