Spend a lot of time with her as kja says, rub her belly and just generally get to know her - it'll make spotting the signs a lot easier

Her udder will start to bag up anything up to a month beforehand, so should be starting to look a bit more developed than normal now. From 2 weeks before her vulva will start to swell, looks like they're in season, but doesn't go after 3-4 days. The milk comes in anything up to 24 hours before farrowing (though we've had colostum from up to a week before) but when it gets to the 'spurting' stage (the slightest touch to the teats has milk coming out) labour is usually less than 24 hours away.
We've used oxytocin on a couple of older sows to help the womb contract (after farrowing problems with their previous litter), but it wasn't given til after the first piglet was born and with a young sow you shouldn't need to worry about it.
Remember to have a couple of cans of stout/guiness/beer on hand to help if she starts to get stressed.
Once she starts farrowing, piglets will arrive roughly 30 minutes apart, I always stay with them when they farrow. Clean the piglets when they come out and either put them under the lamp or onto a teat depending on how mum is. If it gets to over an hour between piglets or it looks like she's in distress then you might have to check her - sometimes all it takes is making sure she gets up and changes sides but other times you might need to go in and rescue a stuck piglet (properly clean hands, lubricant and an anti-biotic jag afterwards if you do)
HTH
Karen
