Contrary to common belief, you can't just play Arms and expect to win by mindlessly throwing a barrage of punches. Sure, throwing punches are needed for victory, but throwing too many will leave any player wide open for the opponent to attack. That is why it's a must to attack with strategy in mind, complimenting your character with the Arms you select and the Abilities they have.
One good trick is to throw out weaker, faster punches with a lighter arm to bait foes into a counter attack, before dashing around them and following up with a much stronger attack. Another good tactic is to use elemental punches that compliment each other, like freezing or stunning an opponent with one Arm and following up with a power attack with another Arm.