You should to good at English do the following ;) That sentence is wrong ,you need lots of practice ,specially the grammar .
Here are some tips for learning English in general.
You can apply several methods, of which to choose the most suitable for you ,that makes you learn easier and quicker .There is no best way, rather several ways to choose from the one that suits you better.
Some of those methods are :
-Reading at your current level of comprehension simple books , articles,magazines, online and offline.
You can look up new words that come your way in the dictionary and write them down .By repeating and reading them now and then it helps you increase your vocabulary .
-Listening to lyrics of songs in English ,watching movies in English etc all helps you get hold of the accent and learn new words and expressions .
-Speaking with native English speakers will help you a lot catch the correct accent and increases your vocabulary and modes of expression. If you don't have the chance to mingle with native speakers in your country you can use online chatting programs such as italki to interact and voice chat with natives .It is a very effective way .
-Doing any activity that involves using English such as games; Scrabble for example is a game where you build words using a crosswords-like board .It is entertaining and you can learn new words through it .
You can look for similar ways to make learning fun!
-Do some grammar exercising using grammar books or online grammar links such as :
www.englishpage.com/ .That would be the theoretical exercise helping you to build correct sentences,then you can apply it by speaking ,reading and writing to better memorize it .
Combining all or some of the above mentioned methods will help you learn and improve your english on the long run ,how long it takes will depend on how much effort and time you dedicate for learning Wish you luck and hope those tips were helpful:)