on the set
There are all sorts of people and departments you need to interact with on the set. As soon as you can, introduce yourself to the entire camera crew: to the ADs; key grip, dolly grip, the rest of the grips; sound mixer and boom operator; script supervisor; camera car or vehicle driver; on set dressers and greens persons; gaffer and electricians; on set painter; and the driver of the camera truck. Wardrobe may lend you special clothing; make-up and hair may want you to pay particular attention to an actor's skin or hair. The special effects people should certainly be talked to if there are any stunts or explosions planned for the day.
The list goes on and on and varies by production. Get the call sheet for the day, read ...