Packing. This one word probably caused me the most anxiety prior to my departure. The only way to ensure efficient and effective packing for a semester abroad is to do your research. The Internet is a great resource to use to initiate this process. Many travel websites provide sample packing lists. Just be aware that you may not need many of the items listed or that something you do need may not be listed. In terms of clothing, simply perform a Google search on the country and city you will be studying in. Many websites provide data about monthly temperature and rain averages. With this data in hand, you can now begin deciding the types of clothing to bring. Packing clothing that can layed and combined to create different outfits is key.
I also recommend going a step further and talking with someone who is familiar with the area; this might include a fellow student, a faculty/staff member, or a family member. Keep in mind that you will be responsible for carrying anything you bring, so pack with your physical limitations in mind. There are two good tests for this. First, carry your luggage up a flight of stairs. Second, carry your luggage around the block. If you struggle with either of these tasks, simplify!
The one thing I wish I would have brought: something to remind me of home.