Before you start working on anything, you should know that you require a comfortable place to sit. Once you are comfortable, you will have a lesser chance of being distracted. A comfortable chair, which is not even too comfortable for you to get sleepy, will work just fine.
A timer is absolutely necessary for you in case you are working on your attention span. You can time yourself whenever you are working on something and that is how you are going to increase your attention span over time. However, make sure that in case you are timing yourself, you do not use a clock that ticks a lot as sometimes you even get distracted with the clock ticking. Therefore, try using a watch that is really quiet and does not distract you when you are concentrating on something.
Meditation is something that can really help you improve your concentration span. Many people fall asleep while meditating, but you should work on your meditation skills as it really helps you concentrate on things that you are working on.
In order to concentrate on things, you need to work on a few exercises and thinking is the best of the lot. Try to think of a colour, image, or even a word and keep thinking about it. Once you concentrate too much on it and once you indulge yourself in one particular thing, you can actually monitor your concentration span during the time you are thinking about that particular thing.
Be patient with the results that are coming your way. It is not totally necessary that once you start using these tools to improve your concentration span, and it will work as a switch. Therefore, be patient and your concentration span will start increasing with time.
For obvious reasons, the only reason why you cannot concentrate on things is because you get distracted too easily. Therefore, make sure that there are not a lot of distractions around you. However, if you do get distracted, try starting your work from the beginning. Moreover, once you have stopped getting distracted for a few minutes, try improving these time intervals over time.