Interning is one of the best ways to gain hands-on experience and really see if a field and industry is right for you. I have had terrible, great, and somewhere in between internships and view each as a learning experience. Every internship comes to an end but there are a few things you need to do that will benefit you in the long run.
1. Write personal thank you notes or emails - Thank you notes and emails are very important. They are a courtesy a lot of the younger generation forget to do and can negatively impact you. The note or email should thank the specific person for their time, guidance, or whatever they helped you with and be sincere. These don't have to be long, maybe a few sentences to a full paragraph. My thank you notes to a senior editor and my boss were much longer and detailed because I worked closely with them and had a lot to say but this is not always the case.
2. Add people on LinkedIn - Your boss, the intern you became friends with, the one executive that took you to lunch or a group of executives that you worked with on a project all qualify as people who should be added to your connection base. LinkedIn is an easy way to keep in touch with these people and they are the kind of people that may help you further down the line when you're job hunting. Don't underestimate the power of a connection on LinkedIn because many people will see who you are connected to that they are and those people how you work and so on.
3. Round up all your work- Portfolios and work proof is becoming increasingly more important as the world continues to shrink and competition continues to increase. Having actual work pieces prove what your resume and you say. Did you design graphics that were used for an email campaign? Take that with you, after asking your boss if that is okay. Did you write up content for tweets? Screen shot those tweets and keep them on file. Your work is a direct reflection of you and can speak louder than anything you might be able to say during an interview.