Start by planning out your day. Make a list of all the tasks that need to be done by the end of the day. This exercise can easily be done when you enter office and are enjoying your morning cup of Joe. Instead of just chatting around different cabins, chalk out this list. It will help you keep a tab on how much time you have and what you need to do in it. Also keep on crossing out the tasks as you finish them.
You may like to visit different cabins to do some office gossip but it wastes a lot of time. This small talk eats up a lot of time and if you avoid it, a lot can be accomplished in that time. If you like to socialize, keep the lunch break for it. Even if other colleagues keep coming to your cabin, show them that you are busy and they will understand. Also try to limit the smoke breaks that you take. It may only seem a ten minute break but when numerous breaks add up, they amount to more than an hour. This leaves a lot less time for work.
If you are asked to stay over time, learn to say no with courtesy. You can tell that you are invited to a dinner or have an important appointment, a dentist visit etc. You can also be honest and tell the boss that you think you will be more fresh and efficient in the morning and you are too tired now. There is no need to feel bad about saying no. You have a life and you should be allowed to enjoy it.
If it is possible, ask an operator to screen your calls before placing them. There are many phone calls which are irrelevant and waste a lot of time. If the operator asks you before passing them on, it will save a lot of time.