http://zzzmirror.i2p/topics/126-how-to-protect-your-identity-on-i2p
This includes IRC, postman's tracker, forum.i2p, other forums such as zzz.i2p and codevoid.i2p, your own eepsites, the eepsite add form on stats.i2p, etc. - In particular, if you ever joined #i2p or #i2p-chat on the non-I2P side on irc.freenode.net, your IP for that nick is known, so pick a different nick for inside I2P.