You should write the Task 2 essay first because it is longer and it is worth 60% of your writing grade.
You should write a minimum of 250 words, but you can write more words as long as they add and expand your ideas. Do not write repetitive ideas or irrelevant ideas.
You should spend about 40 - 45 minutes on this task.
Cause-Effect essays usually provide a trend or something which is happening these days; then they usually ask to whether it is a postive or negative development.
The question usually states:
Causes:Why is this a common trend? ; What factors influence this change?
Effects: Do you think this is a positive or negative develeopment?; What affect does this have on society?
It is more academic and a better strategy to write both positive and negative views.