This is so simple but most folks just box and go, maybe write the room on the box with a marker. The problem is you will likely have dozens and dozens of boxes and they may end up in one big pile. Colored stickers help the movers and help you identify by room.
Designate a color for each room in the new home, such as yellow for kitchen, orange for dining room, etc. Apply colored stickers on the box near the box number. In your new home. Put a matching sticker on the door to each room. The movers will know where to put everything when they arrive at the destination. It’s also helpful to post a big sign on the wall in the room where you want boxes stacked, (“Boxes here please”) to keep them out of furniture and traffic areas.
Good Luck and use those stickers.