Usually there'll be freeleech files or freeleech days etc. This alows you to download without affecting your ratio.
Download a heap of freeleech content ans seed it 24/7. I was on a porn tracker and downloaded a few 20gb site-rips on freeleech. If 5 people download the full site off me, that's 100gb of ratio.
Try download some big files that you'll be one of the few seeds of after a while. If you only download content with 2000 seeders then you'll never get a good ratio, but if you can download some full TV series on freeleech then people will occaisionally want to watch the show and you can seed it to them