I always get a feel for the fight. Initially it seems healers will gauge my loss of HP, which is low ATM as i crawl to 70. So if im at 50% ill pop rampart or convalescence to allow the healer time to get me up. If i pulled a giant wave ill pop all three which gives the healer time to set up and begin healing. As a healer main i try to make it easy for them to keep me alive. Plus if youre not using your cooldowns are you really having fun as a tank?