One trick I learned from the TSE map is that the AI will usually go after a ranged unit. For example if you have 2 cities close to each other, one of your own and one you are about to conquer, you can lure the enemy units towards your own city by moving a ranged unit outside the city center. Then when the AI approaches that ranged unit you will move it back inside the city. Now the AI will go for the units attacking his city and in this point you can again move the ranged unit outside of your own city's center and lure the AI units towards the ranged unit again. Rinse and repeat.