You break the B1/B2 plateau by shifting from passive exposure to active, deliberate vocabulary learning in context, and by pushing your output beyond your comfort zone. Simply watching films or playing games will help maintain your level, but to reach C1 you need to systematically fill gaps in your lexical knowledge and practice using new words in speech and writing.
First, diagnose your weak areas. Take a vocabulary test designed for B2/C1 (many free ones exist online) to see which topics you lack words for. Then instead of random word lists, learn vocabulary in thematic sets: for example, all the verbs and nouns related to economics, or emotions, or technology. Use a spaced repetition app like Anki or a flashcard app to review daily, but always include the word in a full sentence you create yourself.
Second, change how you consume content. When you watch a film or read an article, do not just understand the gist. Pause and write down 5-10 unfamiliar but useful words or phrases. Look them up in a monolingual dictionary (like Cambridge or Merriam-Webster) and note the definition, an example sentence, and any common collocations. Then use each new word in a sentence about your own life within 24 hours.
Third, push your output. Join a conversation group or find a language partner online (there are free exchange platforms). Before each session, prepare a topic and deliberately try to use 5 new words from your recent learning. Record yourself speaking for 2 minutes on a topic, then transcribe it and correct errors. Write short essays or journal entries and ask a tutor or advanced speaker to give feedback on word choice and naturalness.
A common mistake is thinking grammar is fine and only vocabulary matters. At B2, subtle grammar issues like article usage, prepositions, and collocations often hold you back. So take a grammar test or ask a teacher to evaluate your writing for these patterns.
Finally, be patient and consistent. The plateau feels frustrating, but it is normal. Aim for 30 minutes of active vocabulary work daily plus 30 minutes of intensive input. In 2-3 months you should notice a clear shift to B2+ or C1. The key is not just learning more words, but learning them deeply and using them actively.