Sound more natural when you speak and write.
By saying, for example, go blank, rather than forget everything, you won't just be understood, you will - quite rightly - sound like a fluent user of English.

Vary your speech and, probably more importantly, your writing
Instead of repeating everyday words like very, good or nice, you will be able to get access to wider range of language.

Mastering collocations, idioms and phrases means no more struggle, pausing or confusion while dealing with any of the major skills of the language (writing, reading, speaking and listening). This is the most effective method to use English words in a correct but natural way.