Use the "Magic Shield" item to protect your city from being attacked for a period of time (does not protect troops outside of the city).
You can withdraw troops that are collecting resources if they're attacked.
You can dispatch troops to avoid one attack if your city is under attack.
Use movement items to flee from the chaos and your enemy won't know about your new location for a while.
Build enough hospitals so that your soldiers will be wounded instead of being killed in battle. In this way, you can send wounded soldiers back to battlefield while expending the shortest time and fewest resources possible.
A leage is always a powerful form of insurance. Allies can send support to garrison in your city. Your allies can support you more easily when you are located nearby.