Well, we people always think about something or another each and every second of our life, and we couldn't concentrate on a specific thing every time we try to focus on it, its mainly because our attention span is very weak, its a big problem for school and college students because since they couldn't concentrate more on studies they can't able to score high in exams. lets see how to improve our concentration levels to the peak extend as possible.
Just observe your brain that how it works, brain has its own opinion, always it thinks of unnecessary things, observe what is going inside the mind and try to control it. when you started to think brain is just part of your body, you can able to concentrate more on things.
ie) When you are studying or watching television, when a bike passes by in the road you could able to hear it, its just a distraction sound, you should try to control distractions.
Many of us used to think on the past rather than the present. ie) A man going to office thinking of the fight happened during the morning with his wife and doesn't concentrate on the work.
Some of us used to think about the future then living in the present. ie) A college student thinking of his future about where he is going to join a job after graduating, instead of concentrating on the current studies.
Live in present
To live in present, use the power of now, to bring complete concentration, u can do meditation. while doing some work like eating, washing your hands in water, feel the taste of food and eat, feel the coldness while washing the hands. then slowly your brain will start to adopt it and becomes a habit.