Reading books and watching videos that are at the right level are two enjoyable and highly effective ways to improve your English.

Reading - make sure that it comprehensible, not too easy or too hard. You should already know 70%-95% of the words.

Videos - it helps if they have lots of visual cues to help you understand what is being said. It isn't necessary to catch every word or phrase.

Below is a list of materials that are good for learning English.

Books

Let's Read Asia - Picture books that you can sort by difficulty.
StoryWeaver - Pictures books that you can sort by level.
Epic Books - A paid service that is free for teachers.

Videos

Beginners

Intermediate to Advanced