I was in EXACTLY the same boat with 2nd (now 5 weeks old) - had C-section for 1st (breach), with no labouring whatsoever (not even Braxton Hicks) so had no idea what to expect.
At 39 weeks OB told me that nothing was happening, and that if nothing was happening in a week then we'd talk about another C-section (the hell we will, was my reaction!!)
At 39 weeks 6 days I woke up at 2am with a sore back but thought nothing of it, when I started having pains I assumed they were BH. Hospital was over an hour away so at 11:30am I saw local GP who gave me an internal and said nothing was happening so I went home and walked through the pain. By 2pm I was clock-watching: pains every 5-8 minutes, some taking my breath away. Hubby got home at 5pm and told me to call hospital, when I got to hospital at 7pm I was already 3cm dilated and she was born 1:32am the next morning (on her due date!)
Up until I called the hospital I stupidly assumed that it was just BH, figured the GP knew more than I did!
Meanwhile, I hadn't had any signs prior to that 2am wake-up, less than 24 hours before she was born, so things can happen pretty quickly once they do start.
In my hurry to start things along after my 39 week appt on the Monday, I spent a lot of time on the internet researching (and deciding that some of the ideas, like primrose oil capsules inserted vaginally, didn't suit me!) Tuesday I went for a big walk and Thursday night I spent a lot of time bouncing on my fitball and rocking and leaning forward over it on all fours. Not sure if any of this helped, but Friday morning I woke with back pain and she was born Saturday morning!
Oh, also the Saturday before I went out dancing as my not-quite-Baby Shower (called it my 'Bump Bash'). Hit the dance floor at a nice pub, danced and jumped so much the bouncer told me he didn't want to have to deliver the baby. I can say that I felt bub move further down while I was dancing!!
Good luck with it...