The most important piece of advice for an English learner is to get lots of input. But not all input is the same. There are, roughly speaking, two basic types of English input: formal and informal.
Formal English is used in “serious” texts and situations — for example, in official documents, books, news reports, articles, business letters or official speeches. Informal English is used in everyday conversations and in personal letters.
Here is an example of formal English that you might come across in a book