1. Work in chunks
You need to divide your work in to small chunks of tasks. This would keep the boredom miles away from you. Take one chunk at a time and try and finish that. You will feel the work load reduced as you complete it chunk. This way your mind would get some deserved relaxation from stress.
2. Reward yourself for your determination
After you complete each chunk of your work. Get a short little break to help your mind get some time to rejuvenate. Do something which you love. Play a game of darts, do some social networking stuff like Facebook or twitter, or do answer questions on Stack Exchange (This is my personal preference :] ). But at the same time please make sure that you don't do this things for too long. If you do this for too long then you may loose your focus from your work. So keep a check on your time, as these things can be addictive. Overdoing this can have opposite effects.
3. Find the right Music
You need to check which kind of music helps you be more focused for a longer time and concentrate more. This would also keep your boredom away. I personally prefer soft music in background while I work. Or if it is in office, you can plug in your headphones and stay focused. Also this would enable you to focus more by 30% - 40% at least. This is what I have seen in most cases.
4. Go Incognito
Sometimes outside interferences do cause loss of focus and hence the whole work takes time because of interruptions. In that case you can put on a notification or status outside your cubicle or cabin as "Do not Disturb, Busy with work". Also on messengers you use, you can put this status. This would help you to stay away from interruptions and concentrate on your work and avoid disturbances.
5. Be interested/passionate about your work.
Last but not the least. Unless you love whatever you do, you won't be able to work for long times with it. Get yourselves engrossed in your work. Take interest in your work rather than taking it as a compulsion. Once you start enjoying your work, you would start spending more time at a stretch after your work and your mind would get trained to do the work for longer period of times with 100% focus on the work.
6. Feel Good
Don't think of yourself as inefficient or unproductive. You need to feel confident and energetic to deliver. Do some meditation in early morning to improve your concentrations. And do some exercise in morning to feel more energetic. Rather than stimulating your mind with Tea, Coffee and other similar beverages, I would recommend to do more meditation to keep your mind focused.
Hope this helps you :)