The easiest thing to do I feel is target the enemy for attacking purposes and use the d pad up and down to select party members to heal. Or select the tank, d pad for healing others and d pad right or left to change to enemies when you want to attack, but leaving focus on the tank. I understand there is a <tt> target of target macro but I have yet to use it since I don't main a whm Mage. Having macros for attacking spells while focusing on tank should auto attack the enemy.