I place earthly star pretty much at pull/on cooldown I use that time to DPS and when tank gets low I make it pop.
You can use it for quick heal group after a big AoE but you might miss the DMG part of the skill.

For position, place yourself between the tank (the anchor of your group) and the BLM (because he won't move much) and you should have everyone in the radius. Anything out of range should get back in range, just tell them