You can get a huge head start on this by doing a search.

It's been discussed many times and some of the best thought and ideas are in the archives.

Bottom line... don't use anything you or she enjoys as a punishment. If you like to spank, or crop, or flog, or cane, (for example) then that is reserved for play.

The worst punishment is usually mundane. Lines written. Time out in the corner. That sort of thing.

As far as offenses warranting punishment are concerned, I think that's unique to each couple and situation.