Use Stoneskin in between monster attacks. Helps the healers from casting a stoneskin and allows them to focus a cast on something else. Great example of this is if a Paladin stonskins during a Titan landslide. They are not the focus of the landslide in most cases, and the party members are moving around. Cast a stoneskin on yourself and lower the next incoming damage.
Works for more bosses not just Titan.