The toughest part of balancing is realizing that any little change will probably affect a lot more than you initially think it will. Since the Egyptians can build wonders cheaper and earlier, is a Wonder Victory too easy for them? If Knights are too powerful, what do you do? If you decrease their damage or hitpoints, perhaps they'll begin losing to a unit type they're supposed to do well against. On the other hand, if their counter unit becomes too powerful, it may end up beating the unit that is supposed to counter it. Hitpoints, damage, and attack speed certainly aren't the only things to consider, either. Cavalry Archers or Light Cavalry may look like weak fighters on paper, but when used properly Cavalry Archers can wreak havoc on an economy, and Light Cavalry are arguably the best units for flanking your opponent's force in the game (pretty significant since units take +100% damage from the side and +50% damage from behind!) Mobility, cost, range, and the time frame a unit becomes available are all important factors to consider.