As Opon4 says use Tor + hidden services Some good advide in Network Forensics Evasion: How to Exit the Matrix http://billstclair.com/matrix/index.html
Use gnupg and deposit "documents" at https://cryptome.org/ wikileaks of course.. (as an exemple)Do not give a traceback to any bit of info that can reveal your identity , your location, your country, your culture etc..
https://www.anonbox.net/
