A coach watching 10 players in a game probably won't correct or even detect most mistakes. You have no choice on defense. Note that defense is easy to teach and learn compared to offense. After working on defensive position and movement, teach defense in each situation from the basket outward . Condition your players.
Conditioning makes a difference.
In the last few minutes of a game, conditioned teams make fewer mistakes and move faster than poorly conditioned teams. Conditioned players are better athletes. All conditioning should involve basketball skills. Transform even kamikaze drills into something useful by making players dribble. Write down your practice plan.