In accordance with this, try to save Resolute Smite to be cast upon an enemy that is going to last-hit - the animations all champions must go through to autoattack forces them to stand still.
Placing Bulwark on an ally under attack is a good way to protect them and regain health.
If you are low on health, throw the shield on and draw aggro from some minions into attacking you for the duration of the shield. The damage done will be negligible in comparison to the heal.
Try using Bulwark before casting your spells as it indirectly increases your ability power.
It is a good idea to cast Bulwark right before using Idol Of Durand. The increased armor will minimize damage, and its healing ability may even allow you to end the move with more health than you started with. It will raise ability power as well as result of his passive, allowing you to increase your damage output.
You can significantly increase the damage potential of Idol Of Durand by using it near high attack speed enemies or when multiple foes are close. Keep in mind that minions are also taunted, and may be used to take more hits with minimal damage.
Cancelling the channel sooner after getting hit 8 times will deal as much damage as leaving the spell to channel for the full duration.
The CC from the ultimate is sometimes more effective than the damage, so channelling the spell for the full duration in order to maximize the duration of the taunt can be beneficial.
Against enemies with tenacity, you may need to end your ultimate early to ensure they get hit.
Idol Of Durand can be used to easily get a kill on enemies pushing your turret, as turrets prioritize enemies attacking friendly champions. Pull an enemy in range of the tower and activate it to get the turret to attack them.
If you notice multiple enemies with Tenacity items or abilities that reduce the duration of crowd control, it will be beneficial to end Idol Of Durand early as they won't be taunted for the entire duration.
Champions with CC reduction include Dr. Mundo, Irelia, Singed, and Trundle; it would be better to use your ultimate on other champions, or to end it early to maximize its potential.
On the other hand, grabbing an extra Meki Pendant along with Chalice of Harmony will give nearly as much (reliable) mana regen as Athene's Unholy Grail for relatively little cost, giving a lot of early game sustain. It can later be used to make the upgrade.
Banshee's Veil is a very strong item on Galio. It increases his magic resistance, ability power, health and helps with channeling the full duration of Idol Of Durand by potentially blocking an interrupt.
Galio excels at tanking spells due to his natural build towards magic resistance; however he still needs to build decent armor unless the enemy team is entirely magic damage based.
Galio has no ability to peel enemy units off others and uses skillshots to attack and his ultimate is his only way to peel enemy units off others, avoiding Galio's skillshots will allow you to focus on enemy units with impunity. Alternatively, a fighter champion with a gap-closer can tank Galio's skillshots and then charge in, avoiding Galio's slow.