When should i take tetanus vaccine?

Depends: If you can't remember it is likely 10 years since your last shot. If activities like gardening expose you to spores you should consider a booster even sooner. If your life ever brings you in contact with infants, you should consider the tdap which adds coverage for pertussis, which adults can get even if immunized as babies. This would prevent you from passing it to a baby.

Normally : Given at 11 years old then every 10 years. Sooner if you sustain cuts from nasty sharp objects if you have not had tetanus shot in the last five years.