As has already been mentioned: Get rid of expensive units as soon as you can (after taking Sinope and Nikaia). In the beginning, you will get along famously with Family Members, Levy phalanxes and ..... slingers. Cheap, deadly units. As long as you stay behind walls, the enemy can't touch you. Pelting them with rocks from behind a defensive wall (phalanx included) can cause a lot of damage. There is no reason whatsoever that you should lose more than the odd battle. If you run short on cash, sell a building that you can spare and rebuild later.