I have been interning at a manufacturing firm for (*hold your breath*) almost an entire year (*release your breath*) now. I know that usually internships are not much longer than 2-3 months, so before you starting jumping to any conclusions, let me assure you that the duration of my internship is purely due to the course structure at my college - and NOT due to any indiscretions on my part!! Now that misconceptions have been cleared, lets move on.
If you haven't yet undergone an internship (you most probably will.. soon) let me explain what it entails. An internship is when an innocent individual - usually a college undergraduate - (a.k.a 'the Intern') goes and works for a company who can get away with paying him a very small salary or often nothing because he hasn't graduated yet. It's basically just working to make someone rich and getting nothing in return - the modern equivalent of slavery, except that it is totally legal (credit Urbandictionary for this definition). Alternatively, an Intern is someone who is hired to do menial monotonous work that you couldn't pay people people to do long term because they would quit or eat a .45 bullet. So they hire some naive college grad to do it until they give up , quit, or eat a .45 bullet.

Internship is one interesting roller coaster ride. For some it can provide a singularly thrilling time while for others it can be most mortifying. But from my 11 months of experience as an intern, I have found that you can
(*hold breath again*) survive internship unscathed and actually have a good time
(*release breath*) if you can follow these simple ground rules.
1. Keep your aims high but be realistic: Most interns start their internships with high hopes and aspirations and usually end up disillusioned and disgruntled when they find those dreams inevitably crushed mercilessly by the corporate world. It is easy to have your aims lowered by the monotony of office work but never forget the reason you are there in the first place. Don't be naive, but be realistic with what you expect to gain from the experience.
2. Know that every office is a political minefield: Politics happens at every office. Deal with it! You will ignore it at your own peril. While some times office politics resembles grownfolks pulling each others hair like toddlers in kindergarten, it does help to be politically savvy. Never take anyone's words at face value.
3. Map the terrain - know your friends and enemies: Know your stakeholders - people who are interested/ affected by your work - and know who are genuinely willing to help you and who are hiding a dagger behind their backs. You NEED friends at the right places - people who can back you up or bail you out. If you don't have them, then make them!
4. Be sociable: Be sociable at work. Don't sit in a corner trying to fly under the radar. You do not wan't to hinder your chances of being hired by acting like a zombie. Most times kust having technical skills is not enough, learn to work with (annoying) people.
5. Send your ego on a vacation: You might have been the most popular/successful person at college having done a load of projects, but that counts for nothing at office. You are nothing but an intern (slave) at the workplace, so be prepared to be treated like one. Do not expect anything special.
6. Think out of the box, Be different: You NEED to maintain a good impression. Do something different (but not stupid) to stand out and to showoff your (better) qualities to your superiors. Convince them that you are indeed special. Impression does count - just like in college.
7. Nobody likes a crybaby: In college, you do an assignment and you get graded for it - its straightforward. But when you are an intern, getting credit is a lot more convoluted. People will trample all over you and finally take credit for all your labour, be prepared for it. You need to be smart to gain credit, but being a crybaby or a loudmouth is not the way to gain it.
If you have got any other tips for surviving an internship, do share in the comments section. Cheers.