After your beginner’s protection expires it can be brutal. However, there are things you can do to prevent this. There are many strategies you can use. Most are time consuming because they involve mass-upgrading and building, swapping, and conquering.
In every city you will need to get your buildings as high a level as possible. Only use guidelines on the extremely long loading times. Once upgraded your buildings will be near or at full power.
Also in every city, you should use all of your spots. It’s your choice but I’d recommend one large block of high level cottages, one large block of high level barracks, and use the small blocks for everything else. Only one or two warehouses are fine if they are at high levels. Once you have all the “Limit One” buildings built if able use extra spots for more barracks.
Every city you own should have an academy. Eventually when you have 10 cities technology level raising will seem quick. However, all academies must be as high a level as possible. You should try to keep all technologies at the same level when possible for near-equal times.
This is where all those barracks come in. Pick a unit other than worker, warrior, or scout, make as many as possible, and share to all barracks. This greatly cuts down training time.
5. Alternate Mayors
To decrease building/destruction/upgrading/training/research times alternate different heroes as mayor. High politics decreases building, destruction, and upgrading time. High attack decreases training time. High Intelligence decreases research time.