The best way is to get an English girlfriend/boyfriend.
I would argue on this one to be honest. Why to force yourself finding a foreign girlfriend/boyfriend, especially if you don't need one or already have one. Besides, there is no guarantee that they'll teach you proper English(my first hand experience, I still at times teach my English boyfriend his mother tongue, spelling in particular).
If you simply want to speak in other language, try spending as much time as possible with foreign people (since we all know that working in the UK means working with many polish people , when one can speak his or her mother tongue). But if you wish to speak it properly, learn the grammar first. Ask somebody who feels at ease with English and can explain some things to you.
Buy magazines and newspapers in English. Use a dictionary if necessary.