Your ratio is what percentage you have given back to others of what you have taken. For example, if you download something, and have a .5 ratio on that file, that means you’ve shared back half of what you’ve taken.
Ideally, you should strive to always seed to 1.0 meaning you have given back the same amount that was taken. In an ideal world, this would assure that no torrent ever has to die. Private trackers may have more specific rules about what ratio you must maintain, either overall (across all torrents you download) and/or on each individual torrent you grab. Check the specific trackers you participate on for their rules.
If you deal exclusively with public trackers, then 1.0 should be your minimum goal.
Personally, I’d put your ratio at 2.0, if you have the available data allowance, and bandwidth. Help others like you’ve been helped, even on public trackers.