My ~/.rtorrent.rc looks like this:
min_peers = 10000 min_peers_seed = 10000 encryption = require dht = on peer_exchange = yes
How can I configure my rtorrent.rc so that I could seed better? (or other tips?)
You should not enforce encryption, otherwise you will not be able to seed for those who don't want or can't use encryption.
But most of the "best" seeding settings are in fact about knowing how your ISP deals with the connection: setting up NAT and opening firewall ports if needed, avoiding commonly blacklisted bittorrent ports, knowing if the ISP is screwing with non-encrypted bittorrent traffic, and so on.
The vuze wiki has a nice list of ISPs and their quirks, a good place to look for information on your ISP, if it's there, of course.
There is also a blog post with some patches to tweak the magic