How can I improve my English language so I can find a job as proofreading?

I agree with experts answer. Thanks for the invitation. 

you got to start by writing your thoughts, maybe you can chat so you can get used to the daily english.

then you start reading articles and don't give up and pass any line you don't understand, you can just re-read it loud and slowly so you will be able to catch the idea more easily

Improve it by reading lots and lots and lots of material on so many different subjects, for me it is a "dull" job .But people differs ..  {{I hate reading, although I love to write. }}

Anyway the only way to improve yourself is by reading tooooooo many articles written by professionals and try to criticize it and learn it from a language point of view. Grammar ( yuk ) , spellings, vocabulary diversity ...and so on.

If you love reading that job is perfect for you. GL!

You should focus on English grammar and increase your vocabulary.

Good luck