My advice is to use several sources / techniques. You can indeed use mobile apps such as the one from
Magoosh. Also, a good idea will be to develop your own list of idioms that will come from the practice questions that you do. For example, you can create flashcards with idioms that you missed (did not know before).
There is also a thread here on gmatclub where people posted several sources in Excel & googlesheets formats with hundreds of idioms. This might be an overkill, but everyone is different.
Good luck with your GMAT journey![/quote]
Thank you for your reply.
I will follow your advice and it sounds that
Magoosh alone is not enough!
Thank you