The Darkmoon Faire starts construction on the first friday of every month. It opens on the following monday. The location switches between Thunder Bluff and Stormwind (or rather, outside the nearest small towns). Among other fun things, the Faire has a Fortune Teller, Sayge. He will ask you two questions, and you must choose your answer. Depending on which answers you choose, you receive different buffs. Buffs last for 2 hours, and you cannot receive another buff for an extended period of time. They do not persist through death, so be careful with them.

The three most useful overall are:

+10% damage — answer 1 and 1 (this applies to both physical and magical damage)
+10% stamina — answer 3 and 1
+10% intellect — answer 2 and 2

Here’s the complete list.

1 + 1 = 10% Damage
1 + 2 = +25 Magic Resistances
1 + 3 = 10% Armor

2 + 1 = 10% Spirit
2 + 2 = 10% Intellect
2 + 3 = +25 Magic Resistances

3 + 1 = 10% Stanima
3 + 2 = 10% Strength
3 + 3 = 10% Agility

4 + 1 = 10% Intellect
4 + 2 = 10% Spirit
4 + 3 = 10% Armor