Idioms are certainly tricky in any language. I agree with the previous comments. Remember that languages are always changing. Idioms that were popular 50 years ago may not be as popular nowadays. Always verify idioms with a native speaker. You know what's more important than idioms? Phrasal verbs!!! It's good to focus on a few common idioms, but I'd spend more time on phrasal verbs.

Hi Omar, Learning a language and it's funny idioms can be a challenge. How do children learn these phrases? They absorb them naturally. An adult learner can research specific phrases [as mentioned by A. Goddard] that pertain to your work or hobbies. Once you understand how the idiom fits into a sentence and situation then practice, practice, practice using the phrase. One word of caution - DON'T "Bite off more than one can chew".... :)

If you want to understand written and spoken English then you may need to learn some of the most common idioms. How can you find out which are most common? You could ask a teacher or an exchange partner to tell you which ones from a given list are most common... or you could type the idioms from the list into Google search engine and see how many references there are to each idiom.