Jamil Akhtar

I learnt to speak the British accent by:

1. Listening to BBC Radio; was the first task I did when I wanted to acquire the British accent. 
2. I watched a lot of British series, especially the classic ones. 
3. I downloaded few dictionaries of British Slangs 
4. An English dictionary with the British and American accent, and a tad knowledge of International Phonetics Alphabets.
5. I took a text from classic British literature, recorded it on the phone, listened to them and compared it with the actual British accent. 

The above mentioned are the simplest way to learn British accent and British way of communicating. 

Hi!
It depends on what level of English language speaking you are at. Suppose you are at the primary level where you are unable to make proper sentences structures. Then you must start working on your grammatical part.
If you know the rules of grammar but do not know or lack the confidence to speak. Start speaking to yourself first. Start talking to yourself means you need to think about everything in English. Of course, your mother tongue is not going anywhere from you. When you start thinking in English, you may not express it to someone as well. Try a mirror or a friend who too wants to learn to speak English like you. At times you may stammer or make grammatical mistakes, or you may doubt what you have said is right or wrong. So when you have leisure time, check with the grammar when you recall that instance when you made a mistake. Once you have checked it and understand, you may not make a mistake again because you have learned it yourself. It is going to be step by step and bit by bit. Over some time, you will observe that there are changes in your delivery skills.
Try listening to some English radio stations. Better download from google play store.
Do astray reading, and catch words like flying words. It is a fundamental rule for building your vocabulary. It means you do not. Delay finding the meaning of the word you have come across for the first time.
Though it is going to be tedious some times, it will help you improve a lot.
Thanks!

You already have so many grammatical errors in this sentence. But never mind you wrote. It's all a matter of psychology. You just have to think that it's not my mother tongue. When you are learning to speak practice speaking first. Speak, speak and speak. Make a friend who is also interested in learning to speaking English. Converse daily. Do astray reading and listen to BBC radio player. Learn the phrases they use. It's a continuous process. And you will see that over some time you have the grasp on the English Language. And this will boost your confidence also.