Well I have got one handicap, and that is that I am always really quickly fluent in speaking a foreign language. So, I have no real advice for you here. But one thing that is really challenging is making translations. Go and find some (light) news article in English, and translate it to German. The thing here is that you are forced to look for new words and new constructions outside the comfort zone of what you already know.

By the way, about exams, I know that exams are just a snap shot of your knowledge, but they are a neutral and exact figure. Hence I like to have that figure. My German friends always say I am totally fluent in German, but they are biased, I would doubt that if my German was crap they would tell me. :)

What Valentin suggested sounds good but I'd suggest to stay away from dialects. German dialects sometimes don't really sound like normal high German.

But if you understand normal colloquial German, why don't you try some more demanding texts or other sources? Read Frankfurter Allgemeine Zeitung or die Süddeutsche Zeitung, science reports (although they might be too difficult).

Write in German (eg argumentations, mediation, summary etc..), chat on a regular base with others in German (orally and written). Just remember what you did to achieve this level in English.  It's just a matter of practice^^

If you find watching regular movies too easy, maybe you could challenge yourself with movies with less general language: historical movies, movies with a lot of slang or with different accents. However, I'm not sure if there are different accents for the German language.

Currently I am not preparing for any exams, I just wanted to put the level as thing that we can refer to. But perhaps in the future I will do the C1 exam, it can help me to motivate myself. You know, that the goal you can reach for.

As for your case Chris I think the best way is to always do some before-exams, so the exam and the level should not surprise you. And if you see that maybe B2 is too low, you check online for C1 exams and see how it goes. Later you can post your written answers here and get the feedback.

Still, I hope that you have done well and the mark on the test doesn't matter it how you perform in this language in real life :) 

Hi Haplo, Are you preparing for the C1 test? The Goethe C1 test?

Actually when I was studying German, I doubted between doing Goethe B2 and Goethe C1. I have done the B2 test a week ago, but it seemed that easy, that I was sorry for not trying C1 in one go. I am not sure it was really easy, though. I have not got the result back. Maybe I am over confident, and the teachers see mistakes I did not see.

Anyway, if you are going from B2 to C1, I am curious how big that step is. Is that test really a lot more difficult?

But, I am finished studying German, and focusing on some other fields I have to study. They are more exact science subjects, no languages for the moment. I kind of hope I get a bad point for B2. I mean, I would like to have passed that test, but not with an 80%++ score. Then I would think I was a coward for not trying the heavier exam.