Well, there are quite a few ways, and I was bitten by a werewolf.......

1.) Get bitten by a werewolf.

2.) Wear the enchanted skin of a dead wolf or werewolf.

3.) Drink water from a wolf's footprint.

4.) Eat dust from a wolf's footprint.

5.) Drink water from certain springs

6.) Drink downstream from wolves.

7.) Possess and wear a moonstone

8.) Eat a wolf's brain.

9.) 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.

10) The 7th of 7 consecutive daughters was supposed to carry
the werewolf strain (from Germany).

11) 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).

12) Children born on the winter solstice or Christmas eve
supposedly had a good chance of becoming a werewolf when puberty was reached.

13) Get cursed by a powerful witch, wizard or god.