Hi Yacine ,
To improve your English and speak i fastly and clear you can apply many methods .You can choose of them the one that suits you more and which makes you learn quicker.
Some of those methods are :
-Reading at your own level of comprehension and understanding (simple books , articles online/offline , magazines).Try always to look up new words in the dictionary to increase your vocabulary .Writing the
new words and reading them loud now and then will help you memorize them.
-Listen to lyrics of songs in English ,watch movies in English and try to learn new words and again you can write them down to keep repeating and reminding yourself of them ,words as well as expressions.
-Speak with native speakers to get hold of the native accent and increase your vocabulary and your modes of expression.If you don't have the chance to meet with natives in your country ,you can use online chatting programs such as italki to voice chat with natives.It is very beneficial.
-Do any activity that involves using English such as games so that learning becomes fun;Scrabble is a game for example where you compete with others in building words using a crossword-like board so it is a game yet a way of learning new words .
-Exercise grammar using grammar books or online grammar links .
Combining the above mentioned methods ,some or all of them will help you improve your english and gradually be able to speak it fast, clear and with minimal mistakes , how long it takes will depend on how much effort and time you dedicate for learning.
Wish you luck and hope these tips were helpful:)