I'm Lisanne, from the Netherlands.
I'd say you can improve your vocabulary by reading texts. On the internet, in books, in English magazines, it doesn't matter. In texts you can often guess the meanings of words you don't know yet from their context.
Also, watching tv can be a way of improving your English, hearing the English words and seeing the translation in the subtitles below can improve your understanding of English.
As for speaking, I'd say the only way to really get better at it, is to practise.
I agree with you that English is important. Internationally it is currently one of the most dominant languages, so it is an advantage to be albe to use it.
I hope this will prove helpfull to you, let me know.