I hope your summer break was as fantastic as mine. I will tell you some details about my vacation soon. But for now, let's get back to business. I've spent some time thinking about ways how to efficiently expand my vocabulary. Here is what I came up with.
Books & Mind Maps

Another Merriam-Webster’s book called Vocabulary Builder is very useful when it comes to learning an entire word family. The words are grouped by family, so for example benefit, beneficent, beneficiary, benevolence, benevolent and benefactor. By remembering the commong root bene, it is easier to memorize the words. At the end of every other unit, there's a short quiz so you can test yourself. As you can see on the picture, I like to create mind maps for those word families.
Another book I would like to mention is the Merriam-Webster’s Guide to Punctuation and Style. This book not only gives me hints and tips about punctuation, but copyediting, quotation, proofreading, word usage and many other topics as well. In spite of all the advantages of such books, and I am also including the Porter Book here, they all have one major drawback: They do not tell you how to pronounce a word. Therefore you need to have an online dictionary handy in order to listen to the correct pronunciation. If I am studying in the train, for instance, and I don't have a laptop with me, learning new vocabulary is almost impossible since I can't listen to the pronunciation properly. This can be quite tiring sometimes.
Online Platforms
When I am online I use online platforms like vocabulary.com or thesaurus.com. On vocabulary.com, in particular, I like to check the use of the word within a sentence. What I also like about the site is that I can create my own vocabulary lists and take vocabulary quizzes.
Corpora
So far, I haven't used various corpora often enough to be able tell which one is my absolute favorite one and which ones I don't like. One corpus I have used a few times, though, is just-the-word.com. This website has a simple and clear structure and the search results are listed in a very neat way. The user is shown a handful of collocations and how frequently a word or phrase occurs in that corpus. Another website I found very useful is the Oxford Learner’s Dictionary and its Academic Word List. This alphabetically ordered list is linked to the definitions of the words which comes in very handy.Books and Newspapers

Another one of my favorites is The Art of Thinking Clearly by Rolf Dobelli. The Swiss author analyses phenomenons of our daily lives which we aren't always aware of. Every once in a while I buy newspapers as they contain loads of vocabulary of a higher register.
Movies and Series
When I watch documentaries or series and I don't understand a word, then I simply guess the meaning of it. So first, I would write down the word, guess what it could mean from the context, and then I look it up in a monolingual dictionary. For example, as I am attending Henry Briscoe's lecture about the Culture of the U.K., I watch a documentary about Great Britain every now and then.
Of course, like almost every student, I watch series. My favorite one is "Pretty Little Liars", although there are currently no new episodes available. I also like watching Game of Thrones (even though I never thought I would ever like this series; I was forced to watch it and then all of a sudden I wanted to watch even more). Anyways... watching (American) series not only helps me a lot to expand my vocabulary, but also to practice my American English pronunciation.
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This is already the corrected version of the blog post I handed in.
I hope you enjoyed the read. Stay tuned! :)