.5:1 is the new standard. So half as much as you download.
The requirement only refers to your total, not your individual ratios. So if one torrent isn't seeding well or at all, you can use another one to compensate for it. So if you'd like to download more, you could, but do so in moderation, of course. Building up a sort of "pool" of resources helps a lot, particularly if you get new/popular torrents to help make up for the less popular ones.
Not really sure when you get warned. I'm fairly sure you're a ways off, having joined only a few days ago. 13gb isn't too bad in the hole, especially if you're proactive about keeping it under control.