First rule of rolling, ukemi, and landing on the ground in general- don’t hurt yourself with the impact on the way down.
Paying attention to the arms, shoulders, neck, and head, the correct position so one does not slam them when landing on the ground.
Landing on the ground vs. throwing oneself on the ground.
Using the hands and arms to asst in the landing on the ground, moving around, changing direction, and picking up training tools on the ground.
Using the hands and arms to move aside anything on the ground before one lands on it.
Forward rolls with two hands, one hand, and no hands.