If you upload your own torrent, you are the only one able to upload, if one person downloads your torrent there will be a demand that only you can fulfill. Once that person finishes downloading, the two of you are able to seed it. If a third person downloads the torrent, they might download from you both at the same time, or if you have a poor connection at the time you might don't even be contacted by their torrent client at all.

All you need to do is just keep seeding everything you download, but you're very unlikely to equally upload every byte you downloaded for all torrents.

Best you can do if you're really aiming to improving your ratio is sticking to freeleech content or uploading your own stuff.