Spells

The spells are divided into 4 types: farming, suport, offensive and defensive.

Farming spells: Kingly gift, Wedding, Happiness, Treasures of the Underworld and Nature’s gift.
They are good to upgrade your building, especially Happiness. Use it in the first week, when you receive the boost in your production. Don’t build harpies, you’ll be stronger if you upgrade your city fast. Later you can boost your resources with happiness to make City Festivals;

Support spells: Divine sign, Call the Ocean, Population Growth, Patroness, City protection and Plague(too much cost for nothing).
Use Call the Ocean and Population Growth everytime you're going to train your army to make ships and troops, respectively. It's a good idea to cast these spells when you're full of resources.
Divine sign and Patroness are really bad in my opinion. First, chariots aren’t good, even though I used divine sign in the beginning, when I have nothing to spend my Zeus’s favor(in the middle game, I recommend building manticores) . Second, patroness send a mix of offensive and defensive units.  City protection is only good if you’re a target of the enemy, this will protect you from earthquakes for example;

Offensive spells: Lightning Bolt(useless), Favorable wind, Earthquake, Heroic Power, Return from the Underworld, Helmet of Invisibility, Aim of the Huntress and Illusion. All the spells listed above, except(Bolt, quake and illusion), are used in attacks.
When you're doing an attack always cast them, this prevent that they get caught by Sea Storm and Zeus's Rage.

Defense spells: Wisdom, Zeus’rage, Sea Storm, Desire, Purification. If the enemy cast a spell in his attack, these spells only work, if Purification is used.
So if it’s a land attack, then Purification + Zeus’rage; nave attack, Purification + Sea Storm. But test your spells first to find out if he casted or not a spell in his attack, because you don’t want to waste your Artemis spell in nothing.. For this reason, Artemis is one of the first gods that you must have.
Use Wisdom when you don't know the type of attack.

Tips:

• Always keep a high amount of favor, like 300 in your temple for each good. So you can defend yourself against enemies.
• Don’t fall in fake attacks. If it passes 10 minutes of the launched attack, so he will not be able to return his troops, then it’s probably a real attack. Wait for the attack to get closer to you, so you cast the spell.
• Always cast spells in your attacks, unless your division is over attacking a target.
• Don’t spend your favor in mythical units, they aren’t a priority in the beginning.