I have been doing CP for some time now, and as my profile suggests I am not good at it, But during this CP journey , I have heard many people say that "Don't solve more than 50/60 problems in a particular difficulty range !" ,I really want to know does this strategy really work or I am the most dumbest person in the world who is doing CP ! Because clearly this strategy isn't working for me!

give some advice about what really should I do to improve my rating ,because I am just fed up!