In general, I wouldn't spend too much time worrying about this. You'll learn the ones that you need to learn naturally from just being in contact with English-speakers. In addition, every English-speaking culture has different idioms. In the US, many expressions come from sports, such as baseball, that few countries outside of the US care about ("home run", "hit one out of the park"). Finally, don't bother because more often than not, it just sounds corny (bad).

Having a strong business relationship is priceless. And if you think about it, a business relationship really is built on the personal relationships between the people of the two parties. Knowing and comfortably using informal expressions and slangs is a requisite for moving your relationship to a more personal and therefore closer level. Being able to joke around like buddies is a sure sign of a closer personal relationship.