How overdue are you? Considering you're not strictly overdue till 42+ weeks as Term is classed as anywhere BETWEEN 37 and 42wks according to the World Health Organisation Guidelines.
Here is a link to Natural Induction methods which include Castor Oil which I would not actually recommend, it really just messes with your digestion system and it's not a great idea to give your self the sh1ts, is it?
Walking is great because it helps to shuggle baby down into pelvis and so place pressure on the cervix.
Sex and nipple stimulation is my favourite because it stimulates the hormones of love which are required in labour. So it works with your body and is part of your body, so there can be little to cause problems.