Ask your internship coordinator if there is any project they'd like you to take on or work with. If you see a cool program that your co-worker is creating, ask if you can assist. Just make sure that if you ask for work, you don't complain about being busy when you have a lot of tasks to do!
Ask for Feedback
Ask your boss periodically how he thinks you're performing. Does he or she have advice for how you could better utilize your time? Did he or she approve of your last project? Is there anything you could change about your work? Ask direct questions rather than ambiguous ones. The last thing you want to do is ask how you're doing and get a generic "well" or "great" from your boss.
Follow Through
When your boss assigns you work, complete it to the best of your ability in a timely fashion. Don't drop an assignment because it doesn't interest you or is too difficult. This experience is meant to help you grow and will allow you to expand your abilities. Take the time to learn new skills and to explore unfamiliar concepts.
Focus
Social media should not be a part of the work day unless you're on your lunch break or you are in charge or the social media outlets for your company. Even if you think you can multitask, designate Twitter and Facebook as after work activities.