The best way to clean contacts that I have ever found is to use DeoxIT products on a quality microfiber cloth (the kind sold in camera shops for lens cleaning). If the contacts look clean the product you want is: http://store.caig.com/s.nl/it.A/id.1609/.f?sc=2&category=292 Put a drop of the DeoxIT Gold on a clean, high quality microfiber cloth and gently rub on the contacts. That's it. While I had it out I would do the same thing for each my lenses with contacts, too.
If the contacts actually look dirty (pretty unusual with cameras and lenses), then they should be cleaned before using the DeoxIT Gold. In that case use DeoxIT D-Series contact cleaner first, followed by the DeoxIT Gold. Application method should still be the same - put a small amount on a quality microfiber cloth and gently rub the contacts.