Ways of becoming a Were, from Native American Mythology, from folklore, and from fantasy...

A few ways to become a were, from Native American mythology

(Note: This uses wolves as an example. Any other animal may be substituted, however.)

Be called by the wolf spirit.
Transformation by the Gods (also appears in Greek myth of Lycan, hence the term "lycanthrope".)
Have a vision of the wolf spirit on a dream-quest.
Have a Dreaming that one is a wolf or running with wolves.
Have a dream of the wolf spirit.
Perform a ritual taught by one's animal spirit.
Be cursed by a shaman.
Perform a ritual invoking the wolf spirit.

Get bitten by a werewolf.
Wear the enchanted skin of a dead wolf or werewolf.
Drink water from a wolf's footprint.
Eat dust from a wolf's footprint.
Drink water from certain springs, especially in the Harz Mountains in Germany.
Drink downstream from wolves.
Possess and wear a moonstone (supposedly not all would do it, perhaps an extra enchantment was required?)
Eat a wolf's brain.
Sleep outside on a Friday night when the light of a full moon can shine on your face while you sleep. This one seems to have originated in Italy.
The 7th of 7 consecutive daughters was supposed to carry the werewolf strain (from Germany)
Pluck and wear a rare white marsh flower (the flower's name is supposedly lost, but this method comes from the Balkans so it is probably a species that either grows or grew there).
Children born on the winter solstice or Christmas eve supposedly had a good chance of becoming a werewolf when puberty was reached.
Get cursed by a powerful witch (see Circe) or wizard or god (eg Zeus doing so to Lycaon).
Have sex with a werewolf and survive.
Participate in the rituals of a secret society, such as one among the Nootka Sound natives.
In shamanistic ritual, gain the wolf as your totem animal (or guardian or familiar or whatever applies to the tradition in question) and from this the ability to assume its form. This method would also probably include those who gain such a spirit through meditation or dreams. This is the source for many "spiritual werewolves".

part from 'the basics' from 'What is alt.horror.werewolves' - see also 'Links'