Another thing that can help is to only download part of a new multi-file torrent: For example, if a torrent has multiple files and total size of 10 GB, I find that if I select only 5% of those files for downloading, I'll get them quickly and then seed them back to other users at a high speed.
Fan site torrents are especially good for this. There was one about a week ago where I did this, and my share ratio for that torrent alone is about 13 right now. I'll probably keep it for another week and then delete it.
The only downside to this approach is that this torrent will count against your allowable download slots even when you've downloaded everything you selected. I think that's a small price to pay for pumping up your ratio.
Good luck with this, and let us know how it turns out for you.