With rammus you want to keep the battle going so you use taunt on them and then when they begin to run you slow them down with exhaust, clarity is just for keeping your mana level up in times of need such as you need to taunt them but your out of mana.

Initiate fights with powerball then as soon as it hits you quickly swap to defensive ball curl. Catch fleeing enemies with taunt and then activate tremors right in the middle of the group of champions

Note: This rammus build is built for 1v5