6 beers usually works well.
Practice every chance you have. Be aware of the typical traps for Norwegians when speaking English. "The" and "V" sounds are tough.
I perfected my accent while living in Oslo with an English speaking room mate. (I now live in the US and nobody realizes I am not a native. Sometimes I wish I had my accent back, it was great for meeting people.
Practice, Practice, Practice. If you are flying for a living already listen to all the different accents and determine where they are from. Every European country has their own accent. My favorite is Italian, I hate listening to the French trying to speak English.
I have been trying to get rid of my accent in German. No luck so far. But I do sound better after 6 beers
(At least I think so).