I read that if your body isn't ready it won't happen, however if it's close to ready the following things could quite well give it a little nudge. Here's my list of what I'm doing to prepare for labour:
Perennial massage
To gently stretch and prepare the perineum for labour to reduce the risk of tearing. OH is doing this for me so I can relax into it instead of struggling around the bump.
Evening primrose oil
To soften the cervix. OH is using this on me while performing the perennial massage. He pops open a capsule and uses it as a lubricant of sorts. He also gently coats my cervix with it. I also take one capsule orally per day.
Raspbery Leaf Tea (tablets)
To prepare the uterus for contractions; RLT is meant to give you stronger contractions that go further, so fewer are needed in theory to achieve the same goal. There's no evidence to support this works, but I am a sworn believer; I used this in my first pregnancy and went from 1-10cm in two hours. I started taking one tablet at bedtime from 30 weeks, I brought it up to two tablets at 34 weeks and now I am term I have started taking 3 tablets a day.
Relaxation
Labour won't happen if you're stressed, you need to stay as comfortable and relaxed as you can as much as you can. I use a hot bath, a hot water bottle on my back, a back rub from OH or a crackling fire and a cup of tea.
Essential oils
I have made some 'labour cocktails' of sorts. I bought some lavender, ylang ylang and clarry sage oils from eBay. I mixed a little of each of them with a plain baby oil for massage purposes and mixed some with water in a spray bottle (to spray on me in labour to cool me down or make the room smell all nice and zen). These particular scents are meant to encourage relaxation which will help your labour along. The massage oils OH uses on me now when I complain of backache or sore ankles or whatever and I have another bottle packed in my hospital bag.
Birthing Balls
I have one I sit on for about 30 minutes at a time a couple of times a day, it encourages mum to open her pelvis while sitting comfortably and encourages baby into the best position for birth which will put the needed pressure on your cervix to make it dilate. It also takes the pressure off my spine so my back doesn't hurt for a while.
Walking/keeping active
My midwife told me 'if mum is lazy, baby will be lazy' which loosely translated to keeping active will encourage baby to come. It's getting harder to do much though, I find walking my daughter to school and back twice a day is a huge workout for me now (we go up a very large hill).
Sex
Female orgasms release oxytocin which is the hormone that triggers contractions. Semen contains prostaglandins which softens the cervix.
There are many more but this is all I'm doing for now, if I haven't felt any changes this week I'll be upping my game with some other suggestions