The more you practice, the more your English language improves.
You can use some English-teaching websites. They do not only provide lessons, but they also provide different activities and tests with answers.
Watching English T.V (movies, news, series...), listening to English songs, communicating with native speakers, and reading books are also effective ways that can help you learn the English language.
A good dictionary is also indispensable for learning a foreign language.