So to put it simply just get out there and practice, practice, practice. The pally in my FC is so good at timing his defensive CDs that it takes him forever to drop below 50% health with no heals unless it's a huge hit from a boss; even then he only drops to about 70%-80% only to be healed to full immediately after by one of our healers. PLDs make amazing tanks once they are geared and know their stuff. Good luck!