The ratio is the difference between data sent (Upload /Seed) and data received (Download/Leech).
If you downloaded 1 GB of data, you need to share the same amount of data for a ratio of 1

For proper ratio, it must be based on supply and demand.

It is better to perform .torrent  file transfers, where number of transmitters (seeder) is less important than number of applicants (leechers)
So after retrieving data, you will be in a position to distribute these data to the greatest number and thus create a positive ratio.
Conversely, if you opt for transfers where the number of applicants is less than the number of offers (less than leechs seeds), you will have many difficulties in the ratio, as others propose the same data as you.