Thanks to all who took the time to answer the above question.
Two people got the correct answer I was looking for which was as soon as the basketball was in the air on an attempted shot by the offensive team. Players should look for the offensive player they are guarding. Fine your man and then block him/her out so as to be in position to get the rebound.
Another good answer was when face guarding an offensive player, the only problem I have with that is they cannot help out on dribble penetration if they cannot see where the ball is at all times except when it is in the air on a shot.
By keeping the defensive triangle of you, the ball and the offensive player you are guarding you should know where the ball is at all times except on a shot.
By having the defender point one hand towards the ball and the other hand towards the offensive player he is guarding without the ball this makes the ball, your man and you triangle easy to do to allow the defender to help out on dribble penetration, a back cut or a front cut and if the offensive player that they are guarding gets the ball on a pass.
This was taught way back in the 50’s when I played high school and college basketball.
Hopes this tip helps coaches, players and fans at all levels.