Public trackers aren't as good as Private ones, but they are useful for getting new and popular files easily and without having to seed back.
1) Search public trackers like Kickasstorrents or BTDigg
2) Open the torrent in uTorrent
3) Click the torrent, then the trackers tab
4) Right click one of the tracker entries, and click 'Add Tracker'
5) Copy and paste this list and click OK (you might wanna copy-paste it to a .txt file)
Trackers list courtesy of /r/trackers.
DO NOT USE THIS WITH PRIVATE TRACKERS. YOU WILL BE BANNED