Think about how to approach the question and from there think about how to structure it. Split points into differences which were significant and those that were not along with any similarities. Try to group these into themes. For example, economic, political and cultural. To add nuance to the answer question the premise of the question. For example, consider that there may have been 'many Souths' and 'many Norths'.
Show how one might structure one point. For example, economics: Significant differences Different produce - e.g. agrarian vs industryUrban vs agrarian Bring in some historiography - e.g. Marxist Slave labour vs free labour HoweverBoth North and South were predominately agrarian, the difference was in trajectory Examples of Industry in South, e.g. Tredegar Iron Works in Virginia - challenging the concept of one 'North' and one 'South'The economies of the North and South were interconnected, for example, much of the cotton that was grown in the South was exported from New York in the North
Try to link the points together - for example - different types of economy had political and cultural ramifications.