We covered this in my AP European Class. I could probably get into a lot of detail with you, but I'll stick to giving you a shorter answer.
Basically, the Northern Renaissance took place in areas of Eastern Europe (like the Netherlands). During this time, there was an emphasis on daily life--the lives of peasants. A greater emphasis was put on living a pious, simple life. Therefore, artists like Pieter Bruegel the elder painted pictures such as "Haymaking." It showed regular peasants carrying out their normal everyday tasks. Keep in mind that the Northern Renaissance came much later.
The Italian Renaissance, on the other hand, focused more on the wealthy class (aristocracy). Paintings were elaborate, detailed, and showed how wealthy and powerful people were. This was because a lot of trade was going on during the time of the Italian Renaissance, especially in the Mediterranean. Therefore, individuals were becoming very wealthy, and thus gaining political influence. Also, the Italian Renaissance focused on religion--Roman Catholicism. Popes were wealthy, king-like figures in society and they were often painted in elaborate settings. Greek-Roman revival was VERY important. Oftentimes, paintings reflected themes of the Classical times, and some artists nearly copied the forms of ancient Greek statues and artwork. Also, think of the "Last Judgement." It showed a lot of Italian Renaissance themes. Humanism (the focus of the individual, emphasis on anatomy) , Greek-Roman revival, and religion.
