I'm not sure there is an easy way. There are so many different colloquial expressions and phrases out there, and all dependent on which country they're from too! Perhaps it comes down to just being exposed to them often. Maybe a teacher/tutor would be useful for you to practice with. You can then speak in colloquialisms rather than formal language and it might get easier once you pick it up...

How to drink Coca Cola and don't open the bottle :)?