Speak with Samuel Adams (marked on the map) to begin the mission. As you're looking for him, don't let the guards notice you or they'll attack you because of the third notoriety level. More on that can be found in the chapter of the guide dedicated to notoriety.
The first mission you will get will be tearing off two wanted posters. Doing so you will lower the notoriety level. All poster in the area will be marked on the map with green dots. Tear them off and return to Adams. If you run across any guards, just kill them and finish your task.
From a short cinematic you will learn that you can also lower the notoriety level by bribing town criers or print shops workers.
Optional objective: Do not raise your notoriety to level 3
Your second task will be finding the printers, however before that you will have to go to the sewers with Adams. The entrance will be marked on the map with a green dot.
By pressing the corresponding button you can tell Adams to either follow you or stop. Use that and try to sneak by towards the target while avoiding any patrols. That way you won't have to fight and therefore raise you notoriety level. If you want to obtain full synchronization, the notoriety level cannot exceed level 2.
A fight will be inevitable only after you reach the sewer entrance. Quickly kill the enemies guarding the courtyard and hide inside the hay stack behind him.
After a couple seconds you will be able to leave your hideout and go down into the sewers.