A good activity vs a successful activity

A good activity for an EFL class is one that has

• good, clear instructions
• good reasons to communicate and understand

A successful activity for an EFL class is one that meets your aims for the lesson. 

For example, Pictionnary is a good activity, but if your aim is to teach spelling, it isn't a successful one!  Ordering panels in a comic strip is a good activity; it becomes a successful one if the students draw a comic strip about an event they experienced and have a partner order it using the past tense correctly.