I've been told that sex/orgasm, walking etc.
And I've also heard that you should empty your bladder often, even if you dont feel like you gotta go, because a full bladder can slow down labor's process, or the process of beginning labor at all.
There's also castor oil and nipple stimulation, and i dont really reccommend either of those, they're both extremely uncomfortable and castor oil can be dangerouss.
Hope this helped a littlee.