Both my pregnancy i went into labor early because we had sex we werent looking to have them early but it just made me go in to labor
My god daughters mother went into labour after going swimming and going down a water slide...it worked :)
I've been told that sex, walking, slight squats (don't go down all the way. Do it over the coach or lazy boy chair to make sure I'm not going to hurt myself or baby), nipple stimulation, raspberry leaf tea and evening primrose oil both help dilation and thinning of the cervix, some people say to take castor oil but I wouldn't because it can cause baby to have a bowel movement in the womb and really harm baby.
Google "nipple stimulation" it gave me contractions. Walking and going up and down stairs is good.