As part of the Continuous Education program of the WBA Academy, the WBA International Judge, Gustavo Padilla, explains in the following video the 5 aspects that must be taken into account when scoring a round.
In professional or amateur boxing the goal is to try to connect effective punches to the opponent and avoid being hit, but these punches must be placed only on the vulnerable part of the body (above the belt).
That being said, the five major factors to score a round, in order of priority, are: Effectiveness, Attack, Defense, Technique and Ring Generalship.