This is just a very quick step by step guide on how to sync Ableton Live to Traktor. Very straightforward stuff.
Go to Traktor Preferences > MIDI Clock and set "Send MIDI Clock" to on.
Go to Traktor Preferences > Controller Manager. Create a new generic MIDI device that has an IAC Port as an input and as an output. Add a new Output Assignment, and choose Master Clock >Clock Send.
Go to Live Preferences > MIDI Sync Tab. Make sure that the same IAC Bus port virtual input is set to Input: Sync On. In the case above, it is IAC Bus port 4.
Set Live to external Sync (the EXT button in the top left hand corner).
In Traktor, go to the master metronome section (top left hand corner) and click on the play / pause button under sync. Also click on the "Send" button just above it. Live should automatically sync to Traktor.