If you can watch a movie in english without any subtitles and understand every word, then tell a friend about that movie in english you are pretty close to a 6.
I made the english exams and I have a level 6 which is mostly about understand what is being said to you and to tell that to someone else correctly.
Regarding ATC, know what you need to know, always be prepared for an emergency or something abnormal to happen. If we (pilots) need help, we will ask for it.
NO shortcuts when we are high. Calculate with that we can descend about 300 ft per Nm at low altitude (Below FL100) and not often reduce speed while we are descending.