Since running out of food does not cause your troops to leave/defect having two cities really opens up your options. The most common strategy is the Starve City strategy. One of your cities has mostly farms for resource fields and houses a very small portion of your army giving you a large surplus of food. In your other city you build only one farm so that you can build a stable, the rest of the resource fields fill with equal amounts of the other three resource buildings. This becomes your troop/starve city where you house nearly your entire army. When you want to build troops send food from your food city and use it quickly before your army consumes it all. You can also send wood, stone, and iron back to your food city and build more troops there just make sure to peridocally relocate them to your starve city.