I believe the easiest way to achieve this would be to expose yourself to a lot of British media, and also to make it a habit to exclusively use an English accent when speaking English. You may not get it straight away, but you'll find that with time the accent and pronunciation will begin to feel more natural. As for how long, a month would be enough to see definitive results if you work at conditioning your speech everyday. I'm Kenyan, so having overcome my own pronunciation issues, I understand your sentiment of wanting to have an accent that is easily identifiable and understood globally. Plus it just sounds nice :) Ganbatte ne! (^_^)

correction please

I live in the countryside of Japan. There is a paddy field around may my home. The water enters the paddy field in coming season. At night, the water face surface of the water in the paddy field reflects the moonlight and the flog sings frogs sing. I love this season in Japan.

Celebrities

Every day, we are watching watch various celebrities on TV programs, movies and sports games. Celebrities talk to ordinary people about a lot of information of themselves personal information through TV or radio. Therefore we feel that celebrities are so close to us and we know various aspect of their lives. Though media helps celebrities to gain an audience's reputation, the media is not always on their sides; especially when celebrities disappointed dissapoint people. When this happens, the media ruthlessly attack them.
There are people who believe that the media have has a role to inform genuine figures of showcase genuine information about celebrities. They consider believe that they have a right to know whole everything about celebrities including their private life, like where they are living in, and who their lover is. For them it is seen that seems like celebrities can be more popular and get money by offering their whole lives.
In contrast, other people sympathize with celebrities who are intruded their private whose private lives are being intruded. It is important for them to know their news more about them and aspects which make them popular, for example how many points the sports player scored, or how is the new sing the singer releases the artist's new song is.
In my opinion, we do not need to know all aspects of celebrities' lives and should not intrude upon their private lives. Rude behaviors on behalf of media make their lives change to worse become miserable. We do not have a right to affect other people's lives, even if they are celebrities. Celebrities are equal to ordinary people in terms of value of their private lives. Those who attack celebrities should imagine how they would feel, if they were in the same position as celebrities.

You have a very clear train of thought, well constructed sentences too.

An interview with my boss

I had an interview with my boss the other day .
I set the goal for this half fiscal year with him.
I was recommended for a chance to get the Hazardous Materials Engineer's License class A special group .
However I don't have enough time until the exam takes place, so I have just started to study for class B group 4.
I often become sleepy while studying for the exam.
Does anybody know how to get rid of sleepiness？

And to answer your question, try sneak in at least a 15 minute nap whenever you can every day, and try look for ways to make your studying interesting so that you can stay motivated. 
I hope this helps :)

-Baraka