When learning a language it is especially important to expand your vocabulary and everyone has a different approach in doing so.
For my English class we got the assignment to write about useful vocabulary learning techniques. I believe there are a lot of helpful strategies for learning new words. You just have to find the one that suits you the best.

Online sites
I always use the Internet while learning new vocabulary. It is an effective and easy way to find different language-learning tools. For starters there is a variety of monolingual dictionaries where you can look up specific words and how to properly use them. My favourite dictionary is the Macmillan dictionary because it allows you to search for the explanations and also for the synonyms all at one place.

Reading and listening
If you read a lot, it helps you revisit new vocabulary and see those words in new sentences and contexts. Everytime I read a book and encounter an unknown word I write it down immediately and look it up later. Try to include these new acquired words in new sentences or the next time you write a text. Also when I look up a new words I always search for synonyms. That way you expand your vocabulary even further and it really makes an impression if you use more “fancy” words than just the most basic ones.
Another good learning-technique is listening to a language. Pronunciation is another important step towards mastering a new language. Maybe find a tandem partner and speak to him/her at a regular basis to improve on your communication skills or just watch a TV show.