Personally I never use rams against stone wall citys.. The gates are too well defended...

I just about always use Siege towers... Take the time to build some, maybe even 3 or 4... I often send the time to build extra siege equipment and then take the unit away from it during the setup so it is a sort of reserve..

But for normal stone walls I find a couple of siege towers sufficient unless the enemy has lots of archers... I find one units of archers can usually destory one seige tower in the time it takes for the towers to reach the wall...

You can work around this by spacing your siege towers as wide apart as possible so at least one gets through... Once you have men on the walls you need to start capturing towers and the gates...

For men on the wall, wait until the majority are up the siege tower before sending into a fight unless the enemy are waiting for you on the wall where the siege tower is deployed...

Don't be tempted to try sending multiple units up a siege tower at once as they will get totally tangled up and take for ever to all get on the walls, much better to have a couple of whole units on the wall rather than a portion of 4 or 5 units..

Be very aware of any wall towers that a capable of firing at you troops on the wall (near corners of the wall usually), these need to be captured immediately unless you like wasting your men...

Capture the gate asap so you can bring up more troops... and try and clear the walls of any defenders (pretty obvious that one)...

If the enemy has a lot of phalanx and cavalry waiting inside the gate area make sure you have captured all near by towers and gates as they will fire on the defenders... Also getting your missile troops on the wall is a good idea to clear the inside of the gate area...

At this point you can move you own troops inside the gate and start bringing your troops down of the walls to finish things off..

Note for troops on the walls, be carefull moving multiple units at once as they can get tangled up, block and even knock each other off the wall if it gets crowded enough...

Additionally never, never, never tell a unit to get down off the wall though a tower of gate until the unit is completely on the wall first (no men left climbing the seige tower) as this will completely screw the unit pathfinding and the unit will become unusable...