Learn English quickly - teach yourself English
If you have any basic skills in English you should spend some time exercising and developing your English language skills. There are so many opportunities these days. A lot of people have learnt a lot of English by playing interactive computer games with a lifelike sound track. However, your English language may become somewhat special if you only learn your English by playing games, you might end up talking like a nerd in slang, abbreviations and military terms. So my advice will be to do, or also do, a growing amount of the following:
Read as much English from as many sources as you possibly can. Literature of all sorts, online newspapers, user guides, etc. Listen to podcasts, watch the news and much more in English on TV, etc. Youtube is stuffed with excellent entertaining material, explained grammar and informative stuff, sometimes also disinformation and fake news, unfortunately, so don't forget to be critical and double-check the somewhat dubious information.
You should use a dictionary for at least a number of the words you don't understand. In the beginning you may need an English-Danish dictionary, but later on an English-English dictionary (with audio pronunciation in British and American) will often be sufficient. Take note of new words to build up your vocabulary. But don't destroy your taste for reading by always looking up every other word.
Talk with real humans in English whenever you can, preferably native
speakers of English. In the summertime many tourists will be happy to
speak with you and gain further information about your country and
lifestyle, they often have a lot of questions. A funny and kind remark in
the right situation may be your opening line and will also check if the
tourist(s) would like to talk. Don't hesitate if you think you are not
good enough - they will often help you in a kind way if you hesitate
searching for words.
You could even start a blog or vlog in English to practice your writing
and oral skills, but be sure to check your spelling, grammar, and your use of words. Staying in
contact with international friends on social media is also a good idea,
this will exercise your written skills without thinking for hours.