Rage can be generated in several different ways:
Rage is generated by being attacked. The amount varies based on the warrior's health. Attacks that are blocked, parried, or absorbed (such as with [Power Word: Shield]) also generate rage.
The warrior's auto-attacks (regular melee attacks) generate rage. A set amount of rage is generated by each auto-attack, with off-hand weapons granting 50% of the rage main-hand weapons do. However, special attacks against an enemy do not generate rage (with a few exceptions). By increasing the frequency of a warrior's auto-attacks, Haste can increase the rate of rage generation.
Rage can be generated using certain abilities such as [Charge], [Battle Shout] and [Enrage].