If you drive to Magic Kingdom, park, and take the tram, the Ticket and Transportation Center is where you are let off. You walk by the ticket windows to board the ferry or monorail. It is still a large place, so you probably want to set up a specific place to meet. At least to say, to the far right, far left, etc. Just anything, because it is large. And during mornings, there are thousands of people going through there.
If you are taking Disney transportation, you would have to back track to it by ferry or boat. The Disney busses drop you right outside Magic Kingdom, not the TTC.