Strive for Excellence. Not for perfection.
Some important basics first: none of us will be able to pass an exam in a foreign language without a single mistake. Even at Level 6, this is not a prerequisite. It's more a matter of being confident and fluent in the use of the language in order to be able to communicate efficiently with ATC even in difficult situations. And to make your exam turn out as successful as possible, we put together some helpful information for you:
The first part of the test contains of several questions, that will be played to you from a pre-recorded audio file (see below).

The second part of the test comprises the "open interview". We can literally talk about anything you would like to talk about. It's not about content, it's about consistently controlling both basic and complex grammatical structures and sentence patterns. What did you have for breakfast today? Where have you been on vacation? What is your favourite sport? Please consider carefully, if you want to leave the sphere of aviation related topics or if you find it easier to stick to planes and flying: tell us about your aviation career! Which airplane is your favourite type? What has been the most challenging situation for you as pilot of an aircraft? Have you ever experienced a real emergency? You should mentally prepare the interview thoroughly and have the perfect topic and vocabulary ready to use.
Please have a look at some typical questions as they may appear during the test:
Please tell us about your aviation career!
Many people are afraid of flying. How do you explain your passengers that flying is actually one of the safest ways to travel?
Please describe what you normally do during the preflight check to ensure your aircraft is safe and ready to fly.
Try to be focused and to the point. Take your time. 3-4 sentences are sufficient. It's not about quantity, it's more about structure and well controlled sentence patterns. Ensure that you make correct use of past, present and future tense. Review irregular verbs that you often use!
What does the controller want you to do?
This is about listening comprehension: just explain in your own plain words, what the controller has said.
Spell the letters using the ICAO Alphabet: A – M – Q – L – H
„Alpha – Mike – Quebec – Lima – Hotel“
Spell the following frequencies: 121,5 Mhz and 123,9 Mhz
„One two one decimal five“ and „one two tree decimal niner.“ Bear in mind the ICAO pronunciation "ninER" and "TRee"!
Transponder Code 4293
„Transponder Code four two niner tree“
Alitude 5900 ft
„Altitude fivetousandninerhundred feet“
Prüfung Level 4-6 only: Listen to the ATIS. Which Runway is in use? Which time of the year do you think this ATIS was recorded?
Runway 06 in use. The ATIS was probably recorded during the winter, as the temperature is just minus one degree celsius.
Please describe what you see in this picture. What do you think might have caused the accident?

„I can see a damaged plane, it seems that the nose gear collapsed. The nose gear lies on the ground in the lower left corner of the picture, behind the blue taxi light…this accident may have been caused by…“
Please describe what you see in this picture. What do you think about the flight conditions, potential hazards and threats?

„I can see a passenger plane at the gate, it might be a Boeing 737 but I am not sure. The sky is getting dark and it seems there is thunderstorm coming up. Those storms usually bring strong gusts, changes in wind direction and speed, heavy rain and even hail…“
Please describe what you see in this picture.

„I can see an Airbus A320 that is being pushed back from parking position 306. The weather is nice, sunny and only some clouds. There is a concrete wall in the background…“
We finally recommend to play around a bit with google by searching for mistakes that are typically done when translating from your mother tongue to English. There is plenty of useful information out there, especially about correctly using future, present and past tense, prepositions and adjectives. Especially if your skills are exactly between two levels, these little things could tip the scales and bring you the decisive step forward.