Construct a new identity separate from your real one
Rip out any writable medium (HDD/Flash/USB/FDD)
Use a dial-up modem - no WiFi, no Bluetooth
Boot a seriously stripped-down Linux from a read-only medium
Tin Hat Linux -
Tin Hat | opensource.dyc.edu - is a hardened Gentoo variant that looks good, or compile your own Puppy version.
Store your encrypted data in different "secure" Cloud stores.
Passphrases and codes in a LBB (Little Black Book)
No Twitter, no Facebook, No Google+ or anything like that.
Never book or buy online
Reflash your BIOS before starting every session (UEFI is already infiltrated)
Use an old cellphone (Nokia 6310 is good)
Rent your DVDs
Phone, not SMS if avoidable and then only for trivia.
Use an old 9-pin printer or early inkjet
Write letters to communicate! Read real books and real newspapers!
Tremble!
Mac