how short should I wear it?

Treat it like an essay: long enough to cover the subject, but short enough to keep it interesting

Keep it classy.

Mid thigh

Just above the shoulders

Short enough you have to think before kneeling or sitting.

about ten inches above the knee

as you like.

Hair or skirt?

Hair or skirt?

your nails?

As short as your courage allows..

Not so short that you challenge people in a sexual way. That is disrespectful.