1. How do you know when to use a continuity correction?
If the wording of the problem indicates some rounding, say, to the nearest whole number or if the values of the variable are discrete i.e. whole numbers, then a continuity correction may be needed.
2. Why should I draw a diagram when doing normal distribution problems?
Many people find it easier to visualise the region involved when finding the probabilities, if they have a diagram.
"A picture is worth 1000 words" as they say!