From my experience, once there’s 10 or more seeds, usually my BitTorrent client starts transferring from one or more pretty quickly.
The first thing to try is wait 5 minutes. Unlike downloading from a website, it usually takes a minute or two before BitTorrent finds someone to start downloading from. If the transfer does not start after 10 minutes, then there is something wrong. For example, if the Torrent you’re trying to download is actually a private torrent and you’re not a member of where the Torrent originally came from, this could be the issue.
If this is your first BitTorrent download, try a well known Torrent (such as OpenOffice) that should definitely work to make sure your BitTorrent application is working properly. At least this way you’ll know whether it’s your BitTorrent application, a port forwarding issue (if a warning icon shows in the status bar) or just a problem with the above Torrent you’ve been trying to download.