One of the biggest obstacles that hinders my productivity at work is the constant interruptions that I get throughout the day. On average, I am interrupted about once every hour. While sometimes I welcome the interruption, it can get very frustrating and can often push back my entire day and can cause me to have to work late.
At my office we seem to have created a culture where is it completely okay to just pop in to shoot the shit, ask a question, discuss a project, vent about the coworker that gets under our skin, or just ramble about absolutely nothing at all. When it can take 2-3 times the length of the interruption to get back on track and it happens 3-4 times a day, it can be very disruptive.
I have started to be very conscious of my own behavior and how easy it is to call someone or pop-in "just to ask a quick question" or tell a story, and while it will only take "2 seconds" those 2 seconds often turn into 5 minutes. If everyone in the company popped in, that person would be seeing visitors all day long and not get any work done.
If you find yourself constantly getting interrupted, talk to your coworkers about ways you can all be more productive at work. Suggest "quiet" times during the day when everyone vows not to interrupt unless it is an emergency and absolutely necessary. Create a symbol, such a red slip of paper on your door or outside your cubical, that tells everyone that you can not be disturbed. Get the in habit of requiring all requests to be made via email, with the expectation that you will see to them at certain times of the day. You will not only get fewer interruptions for requests, but you will have a paper trail of what people need form you.
You can also combat some interruptions by altering your work space. Sit with your back to the door so your co-workers need to call for your attention; if they can't catch your eye they will be less likely to interrupt. If you know someone is coming to retrieve a file or report, keep it close to the door with their name on it so they can just grab it and go. If people regularly stop in for documents, always keep those files near the door; a file for each department or individual.
If all else fails, be polite and tell your colleagues that you are very busy and can't chat, but you can spare a few minutes at lunch or your next break. If you don't get paid overtime, you are letting it be okay to have to stay late on your own time to caught up from all the interruptions throughout the day.