40 Common English Idioms ThoughtCo / Hilary Allison By Kelly Roell Thought Co. Learning English isn’t as easy as some might think. First, grammar muddies the waters (makes things unclear), and idiomatic expressions only add fuel to the fire (make things worse). If you’re taking the TOEFL or the TOEIC, or just want to know more common idioms, study this list of 40 common idiomatic expressions bef..